Abstract: Background & objective: Human vertebrae are analysed and measured for various purposes, including to study anatomy, to diagnose illness, and to evaluate therapies. Achieving an accurate morphological and dimensional characterisation of three-dimensional (3D) vertebrae relies on the precise recognition of their features. Traditionally, these features, lacking defined edges, have been identified manually through a time-consuming, poorly repeatable, and poorly reproducible process. To the authors’ knowledge, there is only one method published in the literature able to automatically recognise all the most important vertebral features: the algorithmic feature recognition method (AFRM). It requires a high-density point cloud as input, the presence of all morphological features, even if incomplete, and incurs high computational costs. This research aims to propose an improved version of the AFRM to overcome its limitations. Methods: The proposed approach combines the robustness of AFRM to provide the semantic segmentation of a 3D healthy human vertebra with the ability of the enhanced statistical shape model (eSSM) to transfer information among different models. Specifically, AFRM provides the semantic segmentation of the mean shape of the eSSM, while the latter transfers this information to target shapes. Results: The eSSM was developed using 20 training samples of healthy adult male L2 vertebrae. The test samples included five healthy vertebrae and four vertebras with large missing parts. None of the test shapes were included in the training set. The novel approach could accurately recognise morphological features without the constraints that affect the AFRM. Conclusion: The proposed method guarantees reliable and automated segmentation through AFRM, exploiting the eSSM's ability to provide results even when dealing with sparsely populated or partially incomplete target models, significantly reducing the computational load.

Keywords: 3D medical image analysis | Bio-informatics | Computer methods for vertebra analysis | Shape segmentation | Statistical Shape Analysis

Abstract: In a digital world where technological development allows the implementation of computer-based methods that can objectively support human activities, it is no more conceivable that activities such as the analysis, classification, and reconstruction of archaeological ceramics are made manually. This determines that expert operators are involved in time-consuming, tedious, poorly repeatable, and reproducible activities whose results depend on his/her experience. This problem concerns the need for robust and reliable automatic methods supporting the operator in these activities. To address these problems, in the last years, the University of L'Aquila research group published robust and reliable methods based on the codification of archaeologists’ knowledge in recognizing the most significant geometric and morphological features of sherds. With such tools now available, producing more objective knowledge referring to a huge amount of sherds, the need arises to develop computer-based systems capable of sharing this knowledge. For this purpose, in this paper, a dedicated database is proposed. Particular efforts were made to implement an intuitive and interactive web interface with commands that co-determine the essential interaction of the archaeologist with the fragments in the traditional method.

Keywords: Automatic features recognition | Computer methods in archaeology | Innovative representation scheme | Semantic annotations | Web-based application

Abstract: Over the last few years, significant interest has been addressed in developing computer-based methods to document and analyze fragments of ceramics sherds in archaeology. This is because traditional manual processes do not allow for an objective, repeatable, and reproducible analysis of the large quantities of material needed to fully understand and explain human practices in various cultural contexts, such as the economy, daily life, and the material expression of religious beliefs. In that context, this paper proposes a fully digital methodology resulting from the constitution of an international research group coming from different scientific backgrounds: archaeologists with specific skills and experience in fast 3D geometry acquisition methods and researchers who developed and published the only available computer-based process for recognizing the geometric and morphological sherds features analyzed by archaeologists. The proposed methodology consists of two main parts: 1. 3D acquisition of sherds with the construction of the discrete 3D manifold model based on the Structure for Motion technologies; 2. recognition, segmentation, and dimensional characterization of morphological and geometrical features based on the codification and algorithmic implementation of the knowledge used by the archeologists in the traditional method. The method was applied to analyze a set of 133 sherds excavated at Tell el-Burak (Lebanon) to obtain, through the analysis of the namely Phoenician carinated-shoulder amphorae, new insights into the economic organization of the Phoenician homeland. The method demonstrated the potential for objectively, repeatedly, and reproducibly analyzing large quantities of sherds. Furthermore, it allowed studying sherds by generating new high-level knowledge from those acquired from 3D models; in particular, this paper introduces new morphological features that help the archaeologist classify fragments from an analysis of the rim's shape.

Keywords: 3D archeology | Automatic feature recognition | Hierarchical rims clusterization | Phoenician amphorae | Pottery | Structure from motion

Abstract: The alignment of large datasets associated with 3D reconstructions is still an open issue in the scientific community. Among the several strategies available in the literature, some are based on using geometrical features. In this paper, the Authors have investigated the reliability of associating ideal planes with non-ideal roof features, which may be used to realign 3D terrestrial reconstructions. The obtained results underline a deep influence from noise, which affects the non-ideal roof feature and ideal plane association, and the necessity to define additional experiments to confirm the robustness of the solution.

Keywords: feature-based alignment | marker-less alignment | non-ideal feature approximation | terrestrial point-cloud

Abstract: The paper proposes a new recognition rule to automatically identify the spine line by detecting vertebral apophyses from discrete models of human backs collected by 3D scanning. Unlike previous 3D optical approaches, the process described here aims to directly detect spinal apophyses, following the posturologist’s method. These anatomical landmarks are identified not as areas of the back surface with specific shapes, but by searching for appropriate local shape perturbations. Except for vertebral prominences that are convex regions, spinal apophyses are generally unrelated to specific surface shapes. The rule has been tested on several human backs. For each, an experienced operator identified the spinal apophyses from palpation and indicated their position by applying an adhesive marker on the back surface. These positions are used as a reference to compare the vertebral apophyses automatically localized by the methodology proposed here. The experimental results show that the rule discriminates well even blurred vertebral prominences.

Keywords: 3D optical methods | Local shape analysis | Shape index | Spinal apophyses recognition | Spine line

Abstract: When dealing with craniofacial impairments, restoring the morphological condition is as crucial as restoring the functional ones to avoid psychosocial disabilities for the patient. For this aim, the accurate location of the midsagittal plane is essential for performing reliable symmetry analyses and guiding effective surgery planning. To provide a fully automatic and landmark-independent approach, capable of providing a midsagittal plane for craniofacial skeleton even from anatomical models with high asymmetries, an innovative method, called MaWR-method, was developed by the authors in a previous work. This paper further investigates the MaWR-method by evaluating its capacity to produce a successful outcome even in the worst-case scenario that may be considered in maxillofacial surgery, namely panfacial fractures. In all the test cases considered in this work, the method proved robust and reliable in its original design. It provided a consistent result requiring no user involvement, even when dealing with extreme asymmetries because of extensive and complex fractures.

Keywords: Feature recognition | Mid-sagittal plane | Symmetry analysis | Symmetry plane detection

Abstract: These authors presented an automatic computer-based method for morphological feature segmentation and recognition for thoracic and lumbar human vertebrae in a previous paper. The method analyses high-density discretized models by segmentation and recognition rules codifying the vertebra morphology information, which does not change between different subjects. The methodology has been demonstrated to be valid and repeatable in segmenting and recognizing morphological features of vertebrae. The proposed one gives repeatable and reproducible results concerning the traditional manual methods. Nonetheless, the method has been tested only on human lumbar and thoracic vertebrae without distinctive pathologies. This paper aims to extend this methodology for much wider use by analyzing single vertebrae affected by common defectiveness in archaeological and medical fields. The results of the experimentations, analyzed by a skilled anthropologist and radiologist, show that the method correctly segments the analyzed morphological features, also for thoracic and lumbar vertebrae with defectiveness: in particular, defects that alter the shape of features or the symmetry of the vertebra, determine the absence of a feature, or heavily change the spatial distribution of the anterior part respect to the posterior one, have been analyzed.

Keywords: 3D medical image analysis | Feature recognition | Thoracic and lumbar vertebrae analysis | Vertebrae analysis computer-based methods

Abstract: The study of potteries is still today almost entirely performed manually by archaeologists. The primary limits of the traditional approach are lack of repeatability in the results, the time required for the analysis and difficulty in exchanging information between researchers. Taking advantage of the previous research results obtained by the Authors in this field, a fully automated procedure for the analysis and cataloguing of potteries is presented in this paper. The procedure allows performing the geometric and semantic analysis of sherds, starting from their 3D scanned model. The method can also determine a set of meaningful measurements of the analyzed sherds and classify them according to the analysis results. Finally, the results are collected into a public and web-based application, which can be interacted with by interested people.

Keywords: 3D database | Computer-aided procedure | Pottery analysis | Semantic segmentation

Abstract: In the field of optical 3D scanning for healthcare applications, low-cost depth cameras can be efficiently used to capture geometry at video frame rates. However, the complete reconstruction of anatomical geometries remains challenging since different scans, collected from multiple viewpoints, must be aligned into a common reference frame. This paper proposes a fully automatic procedure to align scans of the upper limb patient’s anatomy. A 3D optical scanner, obtained by assembling three depth cameras, is used to collect upper limb acquisitions. A relevant dataset of key points on the hand and the forearm geometry is then determined and used to automatically obtain a rough 3D alignment of the different scans. Hand key points are identified through a neural network, which works on RGB images captured by the depth cameras; forearm key points are recognized by directly processing the point clouds through a specifically designed algorithm that evaluates the skeleton line of the forearm. The approach was tested on forearm acquisitions, and the results were compared to alternative alignment methodologies.

Keywords: 3D optical scanning | automatic point clouds alignment | depth cameras | upper limb anatomy

Abstract: Developing an automatic process for the segmentation and dimensional characterization of high-semantic level features from a ceramic find is an essential prerequisite for obtaining faster, reproducible, and more accurate measurements than the manual approach. These measurements are essential for analyzing, interpreting, and classifying the archaeological pottery, comparing and analyzing similarities, identifying the presence of standard attributes in the ceramics recovered from a specific archaeological site, or studying ancient manufacturing technologies. This paper proposes a new methodology for the recognition and dimensional measurement of a specific class of geometric features starting from high-density tessellated models acquired by 3D scanners, the Constant-Radius Sweeping Features (CRSFs). The recognition process is performed based on a fuzzy algorithm, which aggregates similar adjacent nodes, according to values of appropriate membership functions, into a single geometric feature. CRSFs are frequently seen in ancient artifacts as convex traces on the ceramic surface, such as plastic and molded reliefs, or concave features, such as engravings, graffiti, working signs, and impressions/stampings. Although they are frequently characterized, from a geometric point of view, by free-form surfaces, CRSFs may also be axially symmetrical geometry: this occurs quite often in archaeological pottery in correspondence with rims, bases, or external walls. In the proposed experimentation, the new methodology is applied to three fragments belonging to the same ceramic vessel and sharing a part of its rim. The results show that the algorithmic implementation of rules for CRSF recognition and measurement enables the automation of the entire process, from feature segmentation to the evaluation of the relevant characteristic dimensions, with the benefit of obtaining more robust and precise measurements than those performed manually. Furthermore, in some circumstances, the methodology proposed here allows for assessing dimensional attributes that would otherwise be impossible to evaluate by conventional methods: this is the case of CRSF not attributable to analytical geometric types, as frequently occurs in archaeological ceramics in the form of decorations, grooves, and processing marks.

Keywords: Computer methods in archaeology | Dimensional features for cultural heritage | Fuzzy logic | Geometric feature recognition

Abstract: igital representations of anatomical parts are crucial for various biomedical applications. This paper presents an automatic alignment procedure for creating accurate 3D models of upper limb anatomy using a low-cost handheld 3D scanner. The goal is to overcome the challenges associated with forearm 3D scanning, such as needing multiple views, stability requirements, and optical undercuts. While bulky and expensive multi-camera systems have been used in previous research, this study explores the feasibility of using multiple consumer RGB-D sensors for scanning human anatomies. The proposed scanner comprises three Intel® RealSenseTM D415 depth cameras assembled on a lightweight circular jig, enabling simultaneous acquisition from three viewpoints. To achieve automatic alignment, the paper introduces a procedure that extracts common key points between acquisitions deriving from different scanner poses. Relevant hand key points are detected using a neural network, which works on the RGB images captured by the depth cameras. A set of forearm key points is meanwhile identified by processing the acquired data through a specifically developed algorithm that seeks the forearm’s skeleton line. The alignment process involves automatic, rough 3D alignment and fine registration using an iterative-closest-point (ICP) algorithm expressly developed for this application. The proposed method was tested on forearm scans and compared the results obtained by a manual coarse alignment followed by an ICP algorithm for fine registration using commercial software. Deviations below 5 mm, with a mean value of 1.5 mm, were found. The obtained results are critically discussed and compared with the available implementations of published methods. The results demonstrate significant improvements to the state of the art and the potential of the proposed approach to accelerate the acquisition process and automatically register point clouds from different scanner poses without the intervention of skilled operators. This study contributes to developing effective upper limb rehabilitation frameworks and personalized biomedical applications by addressing these critical challenges.

Keywords: 3D optical scanning | automatic point cloud alignment | depth cameras | neural network | upper limb anatomy

Abstract: 3D reconstructed models are becoming more diffused daily, especially in the Cultural Heritage field. These geometric models are typically obtained from elaborating a 3D point cloud. A significant limit in using these methods is the realignment of different point clouds acquired from different acquisitions, particularly for those whose dimensions are millions of points. Although several methodologies have tried to propose a solution for this necessity, none of these seems to solve definitively the problems related to the realignment of large point clouds. This paper presents a new and innovative procedure for the fine registration of large point clouds. The method performs an alignment by using planar approximations of roof features, taking the roof’s extension into account. It looks particularly suitable for the alignment of large point clouds acquired in urban and archaeological environments. The proposed methodology is compared in terms of accuracy and time with a standard photogrammetric reconstruction based on Ground Control Points (GCPs) and other ones, aligned by the Iterative Closest Point method (ICP) and markers. The results evidence the excellent performance of the methodology, which could represent an alternative for aligning extensive photogrammetric reconstructions without the use of GCPs.

Keywords: multi-UAV scanning registration | particle swarm optimization | point cloud registration | shape features recognition

Abstract: Ceramics analysis, classification, and reconstruction are essential to know an archaeological site's history, economy, and art. Traditional methods used by the archaeologists for their investigation are time-consuming and are neither reproducible nor repeatable. The results depend on the operator's subjectivity, specialization, personal skills, and professional experience. Consequently, only a few indicative samples with characteristic components are studied with wide uncertainties. Several automatic methods for analysing sherds have been published in the last years to overcome these limitations. To help all the involved researchers, this paper aims to provide a complete and critical analysis of the state-of-the-art until the end of 2021 of the most important published methods on pottery analysis, classification, and reconstruction from a 3D discrete manifold model. To this end, papers in English indexed by the Scopus database are selected by using the following keywords: “computer methods in archaeology”, “3D archaeology”, “3D reconstruction”, “3D puzzling”, “automatic feature recognition and reconstruction”. Additional references complete the list found through the reading of selected papers. The 125 selected papers, referring to only archaeological potteries, are divided into six groups: 3D digitalization, virtual prototyping, Fragment features processing, geometric model processing of whole-shape pottery, 3D Vessel reconstruction from its fragments, classification, and 3D information systems for archaeological pottery visualization and documentation. In the present review, the techniques considered for these issues are critically analysed to highlight their pros and cons and provide recommendations for future research.

Keywords: Automatic features recognition | Computer methods in archaeology | Computer-based methods for sherds classification and reconstruction | Mesh segmentation | Pottery profile detection | Pottery profile dimensions

Abstract: The dimensional characterization of archaeological fragment is a very complex operation and could prove to be useful for identifying the presence of standard attributes in the ceramics found from a specific archaeological site, or for making comparisons and analysis of similarities or for studying ancient technologies used for manufacture of objects. The dimensional analysis of the fragments is now carried out manually with traditional measuring devices. Typically, the results obtained are inaccurate and non-repeatable measurements. This paper focuses on the dimensional characterization of a specific geometric class of features: the constant radius swept features (called here CRS features). Several archaeological features, such as rims, bases, decorative motifs, processing marks and grooves are referable from a geometric point of view to the class of CRS features. These are detail features, which may be very interesting for the investigation of some aspects related to the historical-archaeological classification of the find. CRS features are often found on worn, damaged (e.g. chipped) or fragmented objects; they are frequently characterized, from a geometric point of view, by free form surfaces and by a limited cross sectional extension. In some cases, CRS features can be of axially symmetrical geometry: this occurs quite frequently in the case of archaeological pottery. For all these reasons, it is often difficult to apply traditional manual methods for the quantitative dimensional characterization of CRS features. This paper describes an original methodology for the measurement of CRS features acquired by scanning technologies. The algorithmic implementation of this methodology, consisting of a suitable processing of the feature nodes, allows to carry out automatically the dimensional characterization of the feature.

Abstract: The traditional manual method of analysis of ceramic finds involves expert operators in long and routine activities whose results depend on their subjectivity, specialization, and professional experience. This implies that the analysis of sherds is carried out using few data affected by high uncertainty. These limitations are even more clear with fragments with small axially symmetric portions whose elements of the investigation are not axially symmetric, such as handles, spouts, decorations. In this way both the axis of symmetry of the original object and the reference planes and/or axes of the characteristic dimensions of the elements are identified with such approximations as to compromise subsequent analyses and comparisons. To overcome these limitations, in this paper a new computer-based procedure is proposed. As a case study, the analysis fragments of jugs/bowls with trilobed spouts found in the site of Amiternum, coming from 12th-13th century contexts are considered; their analysis is fundamental to analyze the site where they were found since there is no archival documentation about their use.

Abstract: Motorsports equipment design is a complex and evolving engineering discipline, whose driving factor for each component is maximizing the weight reduction, ensuring its operation and in-service life imposed by the regulations. The design complexity in this field is because all key components are subject to high and time-varying stresses. Top teams in high-tech categories can invest large amounts of money in developing and applying sophisticated CAE systems. Such economic commitment is not sustainable for all those teams operating in strategic categories where the production of vehicles and their components are in the hands of small realities, such as karts or mini-motorcycles. In these fields, the most common design approach is the trial and error on physical prototypes. Such an inefficient approach leads to high costs, and, for the rough exploration of the design space, a very low innovation for every component. To overcome these limitations, the presented paper proposes a systematic methodology for the structural design of high-speed engine parts, accessible also to small artisan teams. The method is based on the use of commercial CAD and CAE software; it analyses a 3D CAD model comprising all the components of the whole kinematic chain to which the element to be considered belongs. The FE model is built by setting appropriate boundary conditions on all the components of the above-mentioned chain and imposing, on the element to be studied, for each kinematic configuration, all the acting loads, including the inertial ones. This methodology is here applied to the redesign of a connecting rod of the engine for go-kart competitions. The obtained results are critically discussed and compared with the key methods available in the literature: static analysis and quasi-dynamic analysis. The results evidence methods presented in the literature do no work in presence of high inertia loads: for some crank angles, the stress level got is higher than the yield stress. Instead, by using the proposed method, the consistency of safety coefficient values with those available in the literature is obtained. The proposed methodology could lead to an increase in innovation and in a time and cost reduction during the development process of the motorsport engines having a high specific power obtained with high rotation speeds. This could determine a decrease in the cost of race vehicles with an expansion of potential practitioners of these strategic categories.

Keywords: Connecting rod optimization | Fatigue | FE model | High inertia loads

Abstract: The sweep features of constant radius are particularly significant for the purposes of the historical-archaeological investigation and classification of ancient artifacts. The paper focuses on the automatic recognition of this specific class of features from triangulated 3D models experimentally acquired from cultural heritage objects. This is not a trivial problem. The ancient artifacts, although repeatable, are unique handmade pieces with a geometry commonly characterized by complex and non-analytical shapes. Their surfaces are also usually damaged and worn, so that the related geometric properties are altered or lost. The methodology proposed here is inspired by the one previously developed by the authors for the automatic segmentation of fillets, rounds and grooves from high-density triangulated models of mechanical components. The paper, in particular, focuses on the aspects of this methodology that must be tuned to allow the recognition of the sweep features of constant radius from archaeological finds. The methodology has been implemented and finally applied to an archaeological find acquired by a laser scanner.

Keywords: 3D archaeology | 3D digital models | Computer methods in archaeology | Feature recognition | Laser scanning

Abstract: The knowledge of the history, economy, and art of an archeological site is based on information that can be taken from ceramics analysis, classification, and reconstruction. The traditional methods used by the archeologists for their investigation are time-consuming, not reproducible, and repeatable, and the results depend on the subjectivity, specialization, personal skills, and professional experience of the operator. An as consequence, only a few indicative samples that have characteristic components are analyzed with wide uncertainties. In order to overcome these limitations, in the last years, some automatic methods for studying archeological pottery’s findings are proposed in the literature. To help all the researchers involved in this field, this paper aims to provide a complete and critical analysis of the state-of-the-art until the end of 2020 of the published methods on pottery classification and reconstruction from a 3D discrete manifold model. For this purpose, papers in English by the Scopus database are collected by using the following keywords: “computer methods in archaeology”, “3D archaeology”, “3D reconstruction”, “automatic feature recognition and reconstruction”, “3D puzzling”. The list is completed by additional references found through the reading of selected papers. The 35 selected papers are divided into three groups: Geometric model fragment processing, 3D information systems for archaeological pottery visualization and documentation, 3D puzzling of archaeological fragments. The results of the present review are focused on the presentation of the pros and cons of the techniques used on these different issues.

Keywords: 3D archaeology | Automatic feature recognition | Computer methods in archaeology | Computer-based methods for sherd classification and reconstruction | Surface segmentation

Abstract: UAV Photogrammetry is a quite widely use technology for 3D reconstruction of territory, thanks to its satisfying results in many fields of applications and its low cost. Most of researches that addressed this topic use Ground Control Points (GCPs) for scaling and georeferencing the acquired point-cloud. In this paper, due to the particular morphology of the surveyed territory that makes very difficult to define GCPs in the region of interest, an innovative technique based on geometrical features was used for orienting, scaling and georeferencing the 3D point-cloud. The case is the ancient Roman outlet of the Fucino emissary, sited in a very steep and not accessible area, near Capistrello (AQ) city, Italy. The obtained results show that the proposed methodology, although less accurate than standard one using GCPs, provides quite good results, so that it can be used where the use of GCPs is difficult or impossible.

Keywords: Archaeology | Feature-based alignment | UAV photogrammetry

Abstract: Ceramics classification and reconstruction are fundamental for the knowledge of history, economy, and art of a site. The method traditionally used by archeologists for their investigation presents a series of significant limitations. The results depend on subjectivity, specialization, personal skills, and professional experience of the operator; hence, they are not reproducible and repeatable. Furthermore, since the method is time-consuming, it is used to analyze only indicative samples that have characteristic components. In order to overcome these limitations, in the last years, some automatic methods for studying ancient pottery’s findings are proposed in literature. All the most promising ones analyze a 3D discrete geometric model of ceramics. By analyzing the voluminous related literature, the hottest topics are 3D geometric model setup, virtual prototyping, geometric model fragment processing, geometric model processing of whole-shape pottery, 3D puzzling of archeological fragments, classification, and additive manufacturing technologies for physical reconstruction of ceramics. In order to help all the researchers involved in this field, this chapter aims to provide a comprehensive and critical analysis of the state of the art for the abovementioned topics. For this purpose, the present review is focused on the presentation of the pros and cons of the techniques used on these different issues.

Keywords: 3D archaeology | Automatic feature recognition | Axis evaluation | Computer methods in archaeology | Computer-based methods for sherd classification and reconstruction | Surface segmentation

Abstract: Background and objective: Because of the three-dimensional distribution of morphological features of human vertebrae and the whole spine, in recent years, to make more precise diagnoses and to design optimized surgical procedures, new protocols have been proposed based on analysing their three-dimensional (3D) models. In the related literature, processes of segmentation and morphological features recognition are essentially performed by a skilled operator that selects the interesting areas. So, being affected by the preparation and experience of the operator, this produces an evaluation that is poorly reproducible and repeatable for the uncertainties of a typical manual measurement process. Methods: To overcome this limitation, in this paper a new automatic method is proposed for feature segmentation and recognition of human vertebrae. The proposed computer-based method, starting from 3D high density discretized models of thoracic and lumbar vertebrae, automatically performs both the semantic and geometric segmentation of their morphological features. The segmentation and recognition rules codify some important definitions used in the traditional manual method, considering all the vertebra morphology information that is invariant inter-subject. Results: The automatic method proposed here is verified by analysing many real vertebrae, both acquired using a 3D scanner and coming from Computerized Tomography (CT) scans. The obtained results are critically discussed and compared with the traditional manual methods for vertebra analysis. The method has proven to be robust and reliable in the segmentation and recognition of morphological features of vertebrae. Furthermore, the proposed automatic method avoids the blurring of quantitative parameters get from vertebrae, resulting from poor repeatability and reproducibility of manual methods used in the state-of-the-art. Conclusions: Starting from the automatic segmentation and recognition here proposed, it is possible to automatically calculate the parameters of thoracic or lumbar vertebrae used in archaeology, medicine, or biomechanics or define their new ones.

Keywords: 3D medical image analysis | Computer methods for vertebra analysis | Shape segmentation | Thoracic and lumbar vertebrae | Three-dimensional measurement

Abstract: From archaeological excavations, huge quantities of material are recovered, usually in the form of fragments. Their correct interpretation and classification are laborious and time-consuming and requires measurement, analysis and comparison of several items. Basing these activities on quantitative methods that process 3D digital data from experimental measurements allows optimizing the entire restoration process, making it faster, more accurate and cheaper. The 3D point clouds, captured by the scanning process, are raw data that must be properly processed to be used in automatic systems for the analysis of archeological finds. This paper focuses on the integration of a shape feature recognizer, able to support the semantic decomposition of the ancient artifact into archaeological features, with a structured database, able to query the large amount of information extracted. Through the automatic measurement of the dimensional attributes of the various features, it is possible to facilitate the comparative analyses between archaeological artifacts and the inferences of the archaeologist and to reduce the routine work. Here, a dedicated database has been proposed, able to store the information extracted from huge quantities of archaeological material using a specific shape feature recognizer. This information is useful for making comparisons but also to improve the archaeological knowledge. The database has been implemented and used for the identification of pottery fragments and the reconstruction of archaeological vessels. Reconstruction, in particular, often requires the solution of complex problems, especially when it involves types of potsherds that cannot be treated with traditional methods.

Keywords: 3D archaeology | Computer methods in archaeology | Information search and retrieval | Measurement precision in archaeol-ogy | Similarity metric

Abstract: The problem of matching fragments of three-dimensional (3D) objects has gained increasing attention, and several approaches have been developed to solve this problem. To date, however, to the best knowledge of the authors, there is no computer-based method supporting archaeologists in this activity. For this purpose, in this paper, a semi-automatic approach is proposed for the reconstruction of archaeological pottery fragments based on two-dimensional (2D) images. Firstly, the method, considering the curves as features, involves the extraction of edge curves by applying the Canny filter algorithm to the fragments’ image. Next, the wavelet transformation method is used to fit the edge curves and obtain the approximation coefficients. Then, the correlation coefficients between fragments are computed and the matching of fragments is done by comparing their values. The proposed approach is tested on some real cases. The results of the experimentation show, if compared with the state-of-the-art, that the method seems to be efficient and accurate in the reconstruction of pottery from 2D images of their fragments.

Keywords: Edge detection | Pottery fragment | Reconstruction | Wavelet transformation

Abstract: Additive manufacturing is a technology for quickly fabricating physical models, functional prototypes, and small batches of parts by stacking two-dimensional layered features directly from computer-aided design data. One of the most important challenges in this sector relates to the capability to predict the build time in advance, since this is crucial to evaluating the production costs. In this paper, an accurate method for obtaining build-time is proposed. This method is based on an advanced GCode analyzer written in Python following an object-oriented paradigm for scalability and maintainability. Various examples are used to demonstrate the reliability of the algorithm, while its potential applications are also illustrated.

Keywords: Additive manufacturing | Build time estimation | Manufacturing costs | Process planning

Abstract: By additive manufacturing technologies, an object is produced deposing material layer by layer. The piece grows along the build direction, which is one of the main manufacturing parameters of Additive Manufacturing (AM) technologies to be set-up. This process parameter affects the cost, quality, and other important properties of the manufactured object. In this paper, the Objective Functions (OFs), presented in the literature for the search of the optimal build direction, are considered and reviewed. The following OFs are discussed: part quality, surface quality, support structure, build time, manufacturing cost, and mechanical properties. All of them are distinguished factors that are affected by build direction. In the first part of the paper, a collection of the most significant published methods for the estimation of the factors that most influence the build direction is presented. In the second part, a summary of the optimization techniques adopted from the reviewed papers is presented. Finally, the advantages and disadvantages are briefly discussed and some possible new fields of exploration are proposed.

Keywords: Build orientation factors | Cost analysis | Multi objective optimization | Part build orientation

Abstract: Potteries are the most numerous finds found in archaeological excavations; they are often used to get information about the history, economy, and art of a site. Archaeologists rarely find complete vases but, generally, damaged and in fragments, often mixed with other pottery groups. By using the traditional manual method, the analysis and reconstruction of sherds are performed by a skilled operator. Reviewed papers provided evidence that the traditional method is not reproducible, not repeatable, time-consuming and its results have great uncertainties. To overcome the aforementioned limits, in the last years, researchers have made efforts to develop computer-based methods for archaeological ceramic sherds analysis, aimed at their reconstruction. To contribute to this field of study, in this paper, a comprehensive analysis of the most important available publications until the end of 2019 is presented. This study, focused on pottery fragments only, is performed by collecting papers in English by the Scopus database using the following keywords: "computer methods in archaeology", "3D archaeology", "3D reconstruction", "automatic feature recognition and reconstruction", "restoration of pottery shape relics". The list is completed by additional references found through the reading of selected papers. The 53 selected papers are divided into three periods of time. According to a detailed review of the performed studies, the key elements of each analyzed method are listed based on data acquisition tools, features extracted, classification processes, and matching techniques. Finally, to overcome the actual gaps some recommendations for future researches are proposed.

Keywords: 3D archaeology | 3D reconstruction | Automatic feature recognition and reconstruction | Computer methods in archaeology | Restoration of pottery shape relics

Abstract: Additive manufacturing (AM) is a group of processes which manufacture a part by adding sequential layers of material on each other. In the last decade, these processes have been extensively applied in industry for constructing small volumes of complex, customized parts. Since parts are built layer-by-layer, the build orientation affects the surface quality and the total cost of the part. The search for optimal build orientation is not trivial since these factors are, typically, in conflict with each other. The major limitation of the methods described in the literature to choose the optimal build direction is in the insufficient accuracy of the estimates of the manufacturing cost and of the surface quality. These factors are very complex to be estimated, and accuracy in their evaluation requires methods that are very time-consuming. On the contrary, in practical use, a multi-objective optimization process requires an objective function that is reliable and easy to be evaluated. In order to overcome these problems, in this paper, original methods to estimate the manufacturing cost and surface quality as a function of build orientation are presented. They are implemented, for the fused deposition modeling (FDM) technology, in a multi-objective optimization problem that is solved by an S-metric selection evolutionary multi-objective algorithm (SMS-EMOA), obtaining an approximation of the Pareto front. The final selection of the recommended orientation is performed by the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method. Properly designed case studies are used to evaluate the reliability of the proposed method, and the results are compared with the state-of-the-art method to find optimal build orientation.

Keywords: Additive manufacturing | Build orientation | Multi-objective optimization | Surface quality

Abstract: The registration permits to positioning in a single reference system point clouds acquired from different points of view. Since this is typically obtained with an iterative numerical method, it represents an important source of error in the entire reverse engineering process. As all iterative methods, such errors depend on the choice of the initial solution; therefore, this process requires an expert user who, by using dedicated software, choices the sequence of clouds to be registered, imposes for each pairwise the first attempt registration, launches the iterative method, and verifies the final result. With the aim to minimize the error and the user's interaction, some devices are proposed in the market (turntable or the anthropomorphic arm, etc.). The above-mentioned hardware and software tools cannot be used in the cultural heritage applications involving large and detailed objects. In this paper, an automatic alignment method of point clouds is proposed. The method uses as inputs the constant radius features, which are frequently detectable on cultural heritage objects. The automatic alignment of the point clouds is based on the recognition, the segmentation, and the registration of the sweep lines identifiable from these features.

Abstract: Additive Manufacturing is a very time consuming technology. An estimation of the build time is fundamental to: Evaluate the production cost in budgeting process.Make use of optimization methods, which use as parameter the build time, for determining optimal build direction. In both these cases a fast and valid build time estimator, which can work with a few input data deducible from geometric model, is required. In the proposed paper a reliable parametric-based method to determine the build time for additive manufactured objects is provided. The implemented method is based on a back-propagation artificial neural network, which gives the possibility to implement the complex functions that elapse some driving build-time factors and the build time. The neural network training is based on data provided by a properly developed analyzer of the list of commands given to AM machines, which performs an analytical estimation of the build time. The implementation of the proposed methodology is illustrated and some comparisons between the real and estimated build-time are provided, then the results are critically analyzed.

Keywords: Adaptive model | Additive Manufacturing | Build time estimation | Process planning

Abstract: Secondary features, such as fillets, rounds, chamfers and grooves, are simple transitions between primary features, generally introduced in order to remove the sharp edges created by the intersection of primary features. Being able to distinguish secondary from primary features is important in various application contexts, such as reverse engineering, automatic geometric inspection of real scanned objects, and for preparation of models for FEM analysis and CNC tool-path generation. The process for the recognition of secondary features from high-density tessellated models of real work-pieces is intrinsically complex for several reasons. This explains why, currently, there are no methodologies able to recognize automatically secondary features and the investigation on secondary features is mostly focused on B-Rep models. In a previous paper, the authors proposed a method for secondary features recognition from discrete geometric models synthetically generated. Here the methodology is extended to discrete geometric models experimentally acquired, for which the recognition is a very complex process, due to the object discretization, to its non-ideal geometry and to measurement errors.

Keywords: Blending features | Feature recognition | Fuzzy logic | Point cloud segmentation

Abstract: Sports equipment design is a young and evolving engineering discipline focused on the best simultaneous optimization of user and product as a system. In motorsports, in particular, the final performance during a race depends on many parameters related to the vehicle, circuit, weather, and tyres and the personal feelings of every single driver. Top teams in high-tech categories can invest huge amounts of money in developing simulators, but such economic commitment is not sustainable for all those teams that operate in minor but very popular categories, such as karts or mini-motorcycles. In these fields, the most common design approach is trial and error on physical prototypes. Such an approach leads to high costs, long optimization times, poor innovation, and inefficient management of the design knowledge. The present paper proposes a driver centred methodology for the design of an innovative mini racing motorcycle frame. It consists of two main phases: the drivers’ feelings translation into engineering requirements and constraints, and the exploration of the design solution space. Expected effects of the application of the proposed methodology are an overall increase in the degree of innovation, time compression, and cost reduction during the development process, with a significant impact on the competitiveness of small racing teams in minor categories.

Keywords: Design methodology | Racing motorcycle frame design | Topological optimization

Abstract: The construction of the artificial emissary of Fucino Lake is one of the most ambitious engineering buildings of antiquity. It was the longest tunnel ever made until the 19th century and, due to the depth of the adduction inlet, it required a monumental and complex incile, which, for functionality, cannot be compared to other ancient emissaries. The Roman emissary and its "incile" (Latin name of the inlet structure) were almost completely destroyed in the 19th century, when Fucino Lake was finally dried. Today, only few auxiliary structures such as wells, tunnels, and winzes remain of this ancient work. As evidence of the ancient incile remains a description made by those who also destroyed it and some drawings made by travelers who, on various occasions, visited the site. This paper presents a virtual reconstruction of the Roman incile, obtained both through the philological study of the known documentation, interpreting iconographic sources that represent the last evidence of this structure, and through the survey on the territory. The main purpose is to understand its technical functionalities, the original structures, and its evolution during the time, taking into account the evolution of the Fucino Lake water levels, technological issues, and finally o_ering its visual reconstruction.

Keywords: 3D virtual reconstruction This research received no external funding | Archaeology | Monumental heritage | Remote sensing

Abstract: Additive Manufacturing (AM) is a technology for quickly fabricating physical models, functional prototypes and small batches of parts, by stacking two-dimensional layered features, directly from computer-aided design (CAD) data. One of the most important challenges in this sector is represented by the capacity to predict in advance build time required for manufacturing a part because it's crucial to evaluate production cost. In this paper, an accurate method for obtaining build time is proposed. This method is based on an advanced GCode reader written in Python following an Object Oriented paradigm for scalability and maintainability. Some examples were used to demonstrate the reliability of the algorithm and possible uses of it are illustrated.

Abstract: Fillets, rounds, chamfers and grooves are secondary features which are typically present in real manufactured mechanical components to satisfy some manufacturing and functional requirements. Despite the broad array of research conducted on feature recognition, the investigation of secondary features is a relatively new topic. All of the pertinent studies have been focusedonly on the recognition of secondary features from B-Rep models. The recognition and segmentation of secondary features from a discrete model is a non-trivial problem due to the same geometric descriptors that may be applied to both primary and secondary features. Moreover, although in real-world mechanical parts primary features are planes, cylinders or cones, the secondary features may be non-analytical and complex-shaped geometries. Further sources of uncertainty are the measurement errors and non-ideal geometries of the real objects to which the method is applied. To overcome these problems, a new and original method to segment secondary features of tessellated geometric models is proposed. The method is based on the analysis of geometric-differential properties and provides specific strategies that reduce its sensitivity to all of the above-mentioned uncertainties without affecting its selectivity. The proposed method, described in detail in this paper, is tested in some very critical cases, and the results are presented and discussed.

Keywords: 3D mesh segmentation | 3D scanning | Blending features | Features recognition | Fuzzy logic | STL

Abstract: The accurate location of the mid-sagittal plane is fundamental for the assessment of craniofacial dysmorphisms and for a proper corrective surgery planning. To date, these elaborations are carried out by skilled operators within specific software environments. Since the whole procedure is based on the manual selection of specific landmarks, it is time-consuming, and the results depend on the operators' professional experience. This work aims to propose a new automatic and landmark-independent technique which is able to extract a reliable mid-sagittal plane from 3D CT images. The algorithm has been designed to perform a robust evaluation, also in the case of large defect areas. The presented method is an upgraded version of a mirroring-and registration technique for the automatic symmetry plane detection of 3D asymmetrically scanned human faces, previously published by the authors. With respect to the published algorithm, the improvements here introduced concern both the objective function formulation and the method used to minimize it. The automatic method here proposed has been verified in the analysis of real craniofacial skeletons also with large defects, and the results have been compared with other recent technologies.

Keywords: Cranio-maxillofacial | Feature recognition | Medical imaging | Mid-sagittal plane | Symmetry analysis

Abstract: The classification of ceramic archaeological fragments is based on shape, dimensions, decorations, technological elements, color and material. Nowadays, all of these features are still recognized and analyzed by a skilled operator. It follows that the resulting characterization of shape and sizes of archaeological fragments is poorly reproducible and repeatable. With a view to overcome these limitations, a computer-based methodology, able to extract automatically several quantitative information from high-density discrete geometric models acquired by the laser scanning of archaeological fragments, was proposed. In this paper, the set of quantitative information obtainable is furtherly broadened, by including the segmentation of some types of morphological features, the identification of the fragment shape type, the evaluation of the longitudinal profile and the estimation of a larger set of dimensional features. Finally, a new 3D information framework is proposed to store the large variety of quantitative information extracted.

Abstract: This paper gives a contribution to the automatic recognition of significant features of ancient ceramics, useful for the historical and/or archeological investigation. These very common type geometric features are obtained by a sweeping action that leaves negative or positive traces, characterized by a cross section with one or more constant radii. The paper proposes a novel methodology that, analyzing the principal curvatures at the points of high-density geometric models of ceramic vessels, acquired by laser scanning, identifies the nodes potentially attributable to these features of constant radius. The recognition process is not trivial since it is affected by uncertainties. To overcome the limits of a recognition based on crisp sets, the recognition rule, proposed for the feature segmentation, is implemented by a fuzzy approach. The method has been tested in the identification of embossed decorations in an ancient olla and it proves to be promising for further applications on other types of geometric features of constant radius.

Abstract: The study of the immense patrimony of ceramic finds is still performed by the traditional manual archaeological approach. So that, the information of the shape and dimensions of the sherds have high uncertainties, are expensive and time consuming to be obtained. With the aim to overcome these limitations, for several years our research group has directed efforts to the development of an automatic computer-based method for the morphological and dimensional characterization of axially-symmetric shards. In this paper, the salient points of this method are reported, as well as the management system of all gathered information. The 3D information system is designed for its future use for pottery classification and reconstruction of ancient ceramics.

Abstract: The Lake Fucino's emissary represents one of the most important hydraulic construction realized in antiquity. Unfortunately, little remains of the original structure of the Roman emissary, obliterated by the Torlonia building and the definitive drying of the lake. This article presents its virtual reconstruction, in order to understand survey and technological issues met by Romans and to visually offer reconstruction theories, interpreting a partially lost evidence of the Roman technology. The engineering resource becomes the means for a deeper comprehension of archaeological questions, combining the tools of engineering and archeology.

Abstract: With the aim to reduce the uncertainties of the traditional archaeological approach and reduce costs for ceramic investigation, in this paper a computer-based method is proposed. A discrete geometric model of a pottery fragment is the starting input, from which a first distinction in axially and not-axially symmetric surfaces can be done. Geometrical and morphological features are then recognized. Only once that all this information is obtained, it is possible to proceed with the dimensional analysis. The analysis carried on the test case here illustrated proves that the automatic method presents accuracy and robustness not achievable even using the best application of the archaeological method. This method seems to be functional to other goals, such as for pottery classification and reconstruction of ancient ceramics.

Keywords: 3D archaeology | Automatic feature recognition | Computer methods in archaeology | Surface segmentation

Abstract: In this paper, a method for determining the best choice of the 3D scanner for cultural heritage applications is presented. Generally speaking, this activity is not trivial since a 3D scanner that matches all the requirements of a typical preservation activity in cultural heritage does not exist. Thus, to the best of the authors’ knowledge, the choice of compromise is typically performed in an unstructured way. In order to structure this choice, a method based on the Analytic Hierarchy Process (AHP) is proposed. In the proposed method, the three levels of the AHP hierarchy structure are the selection of the best 3D scanner for a specific cultural heritage application (goal), the most important technical parameters that mainly affect the choice of a 3D scanner (criteria), and the devices matching the required resolution (alternatives). Having defined the goal, prioritization of the type and quality of information is performed by the team leader of the research group (typically a skilled archaeologist), while the priority of the pairwise comparison among alternatives is decided by an expert on 3D scanners. The application of the proposed method in two contrasting situations concerning pottery fragments highlights its ease of use, its robustness (confirmed by the consistency analysis), and the completeness of the technical and economic assessment (since all relevant elements are taken into account), which put together, in a structured way, competences in very different fields (archaeology and 3D digital devices).

Keywords: 3D archaeology | Analytic Hierarchy Process (AHP) | Choice of best 3D scanners

Abstract: Constant radius geometric features are a common type of manufacturing features of ancient ceramics. They are obtained by a sweeping action of a tool, which leaves negative or positive traces characterized by a cross-section with one or more constant radii. The automatic recognition and dimensional characterization of these features could be useful for understanding the technology used to manufacture ceramics. Thus, a new perspective in archaeological investigations can be furnished. For this purpose, in this paper a new computer-based methodology suited to segmenting constant radius geometric features and measuring their dimensional parameters is proposed. Starting from a 3D discrete geometric model of the ceramic, the region pertaining to these features is determined and measurements of their radii are performed. Due to the uncertainties of various sources, which affect the investigated object, the required process is not trivial. In order to solve this problem, the segmentation phase is conducted using a non-conventional logic suitable for exploring the object with a fuzzy sensitivity, and the measurement is performed by a robust fitting method applied to the segmented entities. The methodology has been tested in the identification of embossed decorations of an ancient olla. The combined effects of the feature segmentation process together with the measure detection approach on the obtained results are critically analyzed and discussed.

Keywords: Computer methods in archaeology | Fuzzy logic | Geometric features recognition | Metrology for cultural heritage

Abstract: A new method for secondary features segmentation, performed on high-density tessellated geometric models, is proposed. Four types of secondary features are considered: fillets, rounds and grooves. Sharp edges are also recognised. The method is based on an algorithm that analyses the principal curvatures. The nodes, potentially attributable to a fillet of given geometry, are those with a certain value for the maximum principal curvature. Since the deterministic application of this simple working principle shows several problems, due to the uncertainties in the curvature estimation, a fuzzy approach is proposed. In order to segment the nodes of a tessellated model belonging to secondary features of a given radius, an appropriate set of membership functions is defined and evaluated based on some parameters, which affect the quality of the curvature estimation. A region-growing algorithm connects the nodes pertaining to a same secondary feature so that, for a given radius, one or more secondary features may be recognized. The method is applied and verified in some test cases.

Keywords: Computational geometry | Features extractions | Fuzzy logic | Mechanical engineering computing | Region growing algorithm

Abstract: The construction of artificial emissary of Lake Fucino's represents one of the most significant engineering challenges that took place in antiquity. Unfortunately, the imposing structure of the Roman emissary was almost completely erased from the building of the late nineteenth century, constructed for the final drying of the lake. This article presents its virtual reconstruction, to understand the technological issues met by Romans and to visually offer reconstruction theories starting from interpreting of the few Roman remains. So that, engineering resources are used to try to understand unresolved issues in archaeology.

Abstract: In this paper, a new method for axis detection of discrete thin-walled axially symmetric surfaces is presented. This method is based on the property of thin-walled axially symmetric surfaces that the minimum path of a point on the external wall to the internal wall is on a straight line passing through the axis. This working principle, since it does not require the evaluation of differential geometrical properties, makes the method robust to noise. The proposed method has been applied in a very critical application area: axially symmetric archaeological pottery fragments, for which the evaluation of the axis is complex because of manufacturing error and of modification of the surface properties due to the action of time and weather. The trueness of the proposed method is compared with those of the five methods presented in the literature in the analysis of real sherds of various dimensions and conditions. The proposed method demonstrates greater robustness than these methods and is shown to be promising to improve the number of sherds that can be successfully analyzed.

Keywords: 3D archeology | Axis estimation | Computer | Geometric inspection | Methods in archaeology

Abstract: Additive manufacturing technologies produce objects which present a characteristic surface texture. This is an inevitable and systematic error and has a predictable shape feature which depends on certain process parameters. In order to reduce manufacturing costs and obtain the best results from the point of view of quality, it is essential to predict this error in advance and choose the process parameters which minimise it. For the purpose of measuring the surface quality, the index Ra (ISO 4287, 1997) is used in the related literature. In this paper, it is first demonstrated that the use of roughness parameters in FDM-manufactured surfaces is not adequate to quantify the surface error. The parameter Pa (ISO 4287) is proposed as a more appropriate index to evaluate the surface quality; it is investigated and critically analysed in comparison with the Ra index. A new original model to predict Pa for FDM-manufactured surfaces is presented. The model prediction is compared with experimental data and with the estimation performed by the models described in the literature, within the limits of their capability to predict Pa.

Keywords: Additive manufacturing | Fused deposition modelling | Surface quality

Abstract: The dimensional characterisation of pottery is usually necessary to typify finds and also to recognise sherds pertaining to the same object. With the aim of reducing the uncertainties that typically affect the measurement carried out by the approach traditionally performed by archaeologists, we propose a new automatic method for dimensional characterisation of pottery fragments. The method, starting from a 3D-scanned high point density model, takes advantages from the preventive segmentation and recognition of its significant geometric features; the corresponding characteristic dimensions are evaluated by dedicated procedures. The dimensions measured are also those typically evaluated by archaeologists. In order to quantify the performances of the proposed method, a comparison of its repeatability and reproducibility is made with respect to the traditional manual approach. The proposed method, tested in some real critical cases, demonstrates better performances and lower uncertainties with respect to the traditional approaches.

Keywords: 3D archaeology | Automatic feature recognition | Computer methods in archaeology | Measurement precision in archaeology | Pottery profile | Surface segmentation

Abstract: For the purpose of reducing uncertainties in the measurements of morphologically complex biological objects, the authors present a new automatic method, which takes advantage from the representation of the object in the form of the 3D geometric model obtained from CT-scans or 3D scanning. In this paper, the method is verified in real cases and compared with the traditional approaches.

Keywords: 3D biomedical image analysis | measurement accuracy | measurement protocols in biomedicine | shape segmentation

Abstract: This paper presents a new methodology whose goals are on the one hand the formulation of a tolerance specification that is consistent with the functional, technological and control needs and, on the other, the automatic control of tolerance. The key aspect of the methodology is the digital model of the product, referred to as GMT (Geometric Model of Tolerancing), which gives a complete, consistent and efficient description of its geometrical and dimensional properties with the aim of being able to specify, simulate, manufacture and inspect them. By means a real test case, the potentialities of a first implementation of the proposed methodology are critically discussed.

Keywords: CAT (Computer-Aided Tolerancing) | GD&T (Geometric Dimensioning and Tolerancing) | Geometric inspection | GPS (Geometric Product Specification)

Abstract: A new method for secondary features segmentation, performed in highdensity acquired geometric models, is proposed. Four types of secondary features are considered: fillets, rounds, grooves and sharp edges. The method is based on an algorithm that analyzes the principal curvatures. The nodes, potentially attributable to a fillet of given geometry, are those with a certain value for maximum principal curvature. Since the deterministic application of this simple wor king principle shows several problems due to the uncertainties in the curvature estimation, a fuzzy approach is proposed. In order to segment the nodes of a tessellated model that pertain to the same secondary features, proper membership functions are evaluated as function of some parameters, which affect the quality of the curvature estimation. A region growing algorithm connects the nodes pertaining to the same secondary feature. The method is applied and verified for some test cases.

Keywords: Computational geometry | Features extractions | Fuzzy logic | Mechanical engineering computing | Region growing algorithm

Abstract: Most universities have introduced 3D CAD education and training in their engineering courses in recent years so as to respond to the actual needs of the industrial world for high-skilled design engineers. It is well demonstrated that the effectiveness of such courses depends on teaching an effective design approach rather than training for the use of specific commercial CAD tools. Since open-source CAD software has emerged in many fields as a promising alternative to commercial off-the-shelf systems, the present paper investigates the possibility for universities to adopt open-source instruments to effectively support their educational goals. Open-source 3D CAD systems are quantitatively evaluated by an original Compliance Index which considers the design tools typically used to model and draw industrial products and their weights in accomplishing the design tasks. The results obtained for the evaluation of a set of open-source CAD systems are presented and critically discussed.

Keywords: 3D CAD | CAD teaching | Open source 3D CAD | Software evaluation

Abstract: This paper presents a method for posture prediction of the upper trunk of video terminal (VDT) operators, which is then verified by means of some test cases. The prediction of the upper trunk posture is, in fact, a very difficult task to carry out due mainly to the complexity of the anatomy of the spine and the surrounding muscles. The method being proposed in this paper is based on the integration of the knowledge which is obtained experimentally through the posture analysis of real cases into a configured human multi-body kinematic model which has been implemented in a commercial CAD system. A trained artificial neural network retains the knowledge concerning the VDT operator’s postures detected in different working positions. The posture simulations obtained with the proposed method are subsequently compared with the real ones determined by a 3D scanner. The results obtained confirm the effectiveness of such a method, which is deemed promising to implement other anthropometric data and further human poses.

Keywords: Artificial neural network | Ergonomics | Multi-body virtual human models | Posture prediction

Abstract: This paper proposes a new automatic approach to determine the accurate measure of human teeth. The aim of the proposed computer based method is to reduce inaccuracy of measurement with respect to traditional approaches. Starting from a 3D model of the teeth which is obtained from 3D scanning, the method algorithmically evaluates the most important dimensional features detectable in central incisors. For this purpose, specific rules are put forward and implemented in original software with a view to identifying repere points, from which to detect dimensional features both unambiguously and accurately. The automatic method which is proposed here is verified by means of the analysis of real teeth and is then compared with the current state-of-the-art methods for teeth measurement.

Keywords: 3D biomedical image analysis | Computer methods for tooth analysis | Dental dimensions | Measurement accuracy | Measurement protocols in biomedicine

Abstract: With the aim to improve the quality of the traditional archaeological approach and reduce costs for ceramic investigation, in this paper a computer-based method is proposed. A discrete geometric model of a pottery fragment is the starting input, from which a first distinction in axially and not-axially symmetric surfaces can be done. Geometrical and morphological features are then recognized. Only once that all these information are obtained, it is possible to proceed with the dimensional analysis. The method here proposed allows reducing the uncertainties of the traditional archaeological approach. The analysis carried on the test case here presented, proves that the automatic method presents repeatability and reproducibility that cannot be obtained even using the best application of the archaeological method. This method seems to be functional to other scopes such as for pottery classification and reconstruction of ancient ceramics.

Keywords: 3D archaeology | Automatic feature recognition | Computer methods in archaeology | Surface segmentation

Abstract: In this paper performance evaluation and experimental characterization of a new automatic method for measuring vertebrae are analysed. Starting to a discrete valid geometric model of the vertebra, obtained from CT-scans or 3D scanning, the method measures algorithmically vertebrae. The proposed study is performed by analysing the most used dimensional features of lumbar and thoracic real vertebrae in anthropological investigations. The results are compared with the state-of-the-art methods for vertebra measurement.

Abstract: In this paper a new automatic approach to determine the accurate measure of human vertebrae is proposed. The aim is to speed up the measurement process and to reduce the uncertainties that typically affect the measurement carried out by traditional approaches. The proposed method uses a 3D model of the vertebra obtained from CT-scans or 3D scanning, from which some characteristic dimensions are detected. For this purpose, specific rules to identify morphological features, from which to detect dimensional features unambiguously and accurately, are put forward and implemented in original software. The automatic method which is here proposed is verified by analysing real vertebrae and is then compared with the state-of-the-art methods for vertebra measurement.

Keywords: 3D medical-image analysis | Computer methods for vertebra analysis | Measurement accuracy | Measurement protocols in biomedicine | Shape segmentation | Vertebral dimensions

Abstract: The geometric segmentation of a discrete geometric model obtained by the scanning of real objects is affected by various problems that make the segmentation difficult to perform without uncertainties. Certain factors, such as point location noise (coming from the acquisition process) and the coarse representation of continuous surfaces due to triangular approximations, introduce ambiguity into the recognition process of the geometric shape. To overcome these problems, a new method for geometric point identification and surface segmentation is proposed. The point classification is based on a fuzzy parameterization using three shape indexes: the smoothness indicator, shape index and flatness index. A total of 11 fuzzy domain intervals have been identified and comprise sharp edges, defective zones and 10 different types of regular points. For each point of the discrete surface, the related membership functions are dynamically evaluated to be adapted to consider, point by point, those properties of the geometric model that affects uncertainty in point type attribution. The methodology has been verified in many test cases designed to represent critical conditions for any method in geometric recognition and has been compared with one of the most robust methods described in the related literature.

Keywords: Discrete differential geometry | Discrete surfaces | Geometric segmentation

Abstract: The present paper proposes a new method for axis identification in discrete axially symmetrical geometric models. This method is based on-a-never-used-before property of the axially symmetrical surfaces for which the symmetry line of any section curve of the surface (or of a portion of it in the case of an incomplete axially symmetrical surface) always intersects the axis of symmetry of the surface. Thus the working principle of the method makes it very robust to local defectiveness, measurement noise and outliers. In order to compare it with the most cited methods presented in literature, several types of tests have been designed and performed. The robustness of those methods, on the one hand, has been evaluated by defining the Statistical Confidence Boundary at 1σ confidence level. The trueness of the method, on the other hand, has been evaluated on geometric models obtained by measuring real objects. The high robustness, which characterizes the proposed method, makes it particularly suitable for product geometric inspection where high accuracy is required.

Keywords: Axis identification | Geometric inspection

Abstract: Axis evaluation is a fundamental preliminary step for several applications, from archaeology to geometric inspection of mechanical workpieces. The axis of symmetry is the situation feature of axially-symmetric surfaces, but also a reference for the evaluation of specific geometric properties (roundness, cylindricity and straightness of the axis). Since it is a non-physical geometric entity, it is not directly measurable from the surface, but can nevertheless be derived from the surface. For discretised models, defined by point clouds or triangular meshes, the axis of symmetry detection is a very complex task to accomplish. In this paper three methods for axis estimation of high-density acquired axially-symmetric surfaces are reviewed and compared in the common cases. The methods comparison, performed in this work, doesn't consist just in an ordinary implementation of methods already described in the literature. These methods involve some auxiliary processing tools (mainly devoted to evaluate geometric differential properties) which characterise the implemented version and its performances. For each of these methods various versions have been considered and implemented which diversify each other for the criterion used for geometrical differential properties of the tessellated model. The methods for axis estimation are compared in the interpretation of the axes of axially-symmetric geometries (analytical and generic, partial and complete) for several types of discretization (size and regularity of the mesh). The results show that in the case of complete axially-symmetric features (analytical or generic), the three analysed methods perform similar results. In presence of not complete axially-symmetric features the methods show very different performances. The methods for axes estimation are of particular interest in several applications where precision and reliability are required. In this paper the main characteristics of the most important methods are identified and some guidelines for their use are given. © 2014 Springer-Verlag France.

Keywords: Axis of rotation | Discretised surfaces | Geometric features recognition | Reverse engineering

Abstract: This paper presents a new mirroring-and-registration method for the automatic symmetry plane detection of 3D asymmetrically scanned human faces. Once the mirroring of the original data is carried out with respect to the first-attempt symmetry plane, which is estimated by the PCA method, the source point cloud and the mirrored data are registered by the ICP algorithm that minimises a new weighted function. The final symmetry plane obtained approximates in the least-squares sense the midpoints of the lines connecting homologous points randomly chosen. This method is validated by analysing some specifically-designed test cases. The obtained results show that the method is quite insensitive to asymmetries of data resulting from the acquisition process. © 2013 © 2013 CAD Solutions, LLC.

Keywords: iterative closest points | mirroring | rasterstereography | registration | symmetry plane

Abstract: A novel self-adaptive geometric primitive for functional geometric shape synthesis is presented. This novel geometric primitive, for CAD use, is specifically designed to reproduce geometric shapes with functional requirements, such as the aerodynamic and hydrodynamic ones, once the functional parameters are furnished. It produces a typical CAD representation of a functional profile: a set of Bézier curves. The proposed primitive follows a generate-and-test approach and takes advantage of the use of a properly designed artificial neural network (BNN). It combines the properties of a geometric primitive and the capability to manage the engineering knowledge in a specific field of application. The proposed evolutionary primitive is applied to a real engineering application: the automatic synthesis of airfoils. Some examples are simulated in order to test the effectiveness of the proposed method. The results obtained by an original prototypal software are presented and critically discussed. © 2013 Elsevier Ltd. All rights reserved.

Keywords: Airfoils design | Artificial neural networks | Automatic design synthesis | Functional shape synthesis | Geometric primitive | Self-adaptive geometric primitive

Abstract: In the last few years the need for methodologies capable of performing an automated geometric inspection has increased. These methodologies often use 3D high-resolution optical digitisers to acquire points from the surface of the object to be inspected. It is expected that, in the near future, geometric inspection will be requiring more and more the use of these instruments. At present geometric inspection is not profiting from all the opportunities attainable by 3D high-resolution optical scanners or from the numerous tools which can be used for processing the point cloud acquired from the inspected product. For some years now, these authors have been working on a new methodology for automatic tolerance inspection working from a 3D model acquired by optical digitisers. In this paper all the information recognisable in a scanned object is organised into a new data structure, called Recognised Geometric Model (RGM). The final aim is to define a representation of the inspected object for the automatic evaluation of the non-idealities pertaining to the form, orientation and location of the non-ideal features of the acquired object. The key concept of the proposed approach is the capability to recognise some intrinsic nominal properties of the acquired model. These properties are assumed as references to evaluate the non-idealities of the inspected object. With this approach the references of geometric inspection are searched for in the inspected object independently of a tolerance specification and of the availability of a 3D nominal representation. The high-level geometric information within RGM depends on the rules used for its identification. The capability to recognise specific categories of nominal references offers the possibility of introducing new tolerances to be specified. The proposed approach has been implemented in original software by means of which a specific test case has been analysed. © 2012 Springer-Verlag France.

Keywords: Automated inspection | ISO tolerancing | Three-dimensional metrology

Abstract: In this work, a new technique for symmetry line detection for non-erected postures, which can not be investigated with the other methods presented in the literature, is proposed. It evaluates the symmetry line by means an adaptive process in which a first attempt is modified step by step until the solution converges to the best estimation. The method here proposed is validated by analysing four different non-erected postures in which the spine does not lie onto sagittal plane, by the comparison with the traditional approach to symmetry line detection, having as reference the cutaneous marking. Results are analysed and critically discussed. © 2012 Springer-Verlag France.

Keywords: Anatomical landmarks | Back shape analysis | Posture prediction | Rasterstereography | Symmetry line

Abstract: This paper proposes a new method for the identification of the symmetry plane of the human face, working from 3D high-density scanned data. The method being proposed is an original variant of a typical mirroring and registration method. This method is validated by analysing some specifically designed test cases. The obtained results show that the method is quite insensitive to local asymmetries, whether they be near or far from the symmetry plane, and is also repeatable and slightly conditioned by the acquisition process. © 2012 Springer-Verlag France.

Keywords: Asymmetry | Mirroring | Rasterstereography | Registration | Symmetry plane

Abstract: The methods for symmetry line detection presented in the literature are typically suited to analyse symmetric upright postures, both standing and seated. The proposed method focuses on the symmetry line detection in subjects assuming asymmetric postures in which this line falls far outside the sagittal plane. The proposed approach evaluates the symmetry line by means of an autoregressive process in order to determine the set of planes suited to slice the back coherently with its geometric spatial configuration. The method is analysed assuming the cutaneous marking as reference and it is compared with a previous one, also developed by these authors. Results are analysed and critically discussed. © 2013 Taylor & Francis.

Keywords: anatomical landmarks | back shape analysis | posture prediction | rasterstereography | symmetry line

Abstract: In a previous paper these authors presented a new mesh- growing approach based on the Gabriel 2 - Simplex (G2S) criterion. If compared with the Cocone family and the Ball Pivoting methods, G2S demonstrated to be competitive in terms of tessellation rate, quality of the generated triangles and defectiveness produced when the surface to be reconstructed was locally flat. Nonetheless, its major limitation was that, in the presence of a mesh which was locally non - flat or which was not sufficiently sampled, the method was less robust and holes and non-manifold vertices were generated. In order to overcome these limitations, in this paper, the performance of the G2S mesh-growing method is fully improved in terms of robustness. The performances of the new version of the G2S approach (in the following Robust G2S) has been compared with that of the old one, and that of the Cocone family and the Ball Pivoting methods in the tessellation of some benchmark point clouds and artificially noised test cases. The results obtained show that the use of the Robust G2S is advantageous, as opposed to the other methods here considered, even in the case of noised point clouds. Unlike the other methods, the one which is proposed preserves manifoldness and geometric details of the point cloud to be meshed. © 2013 CAD Solutions, LLC.

Keywords: Reverse engineering | Surface reconstruction | Triangular meshes

Abstract: In this work, a new technique for symmetry line detection for asymmetric postures, which can not be investigated with the other methods presented in the literature, is proposed. It evaluates the symmetry line by means an adaptive process in which a first attempt is modified step by step until the solution converges to the best estimation. The method here proposed is validated by analysing four different asymmetric postures in which the spine lies far outside the sagittal plane, having as reference the cutaneous marking. Results are analysed and critically discussed. © 2012 Springer-Verlag.

Keywords: Anatomical landmarks | Back shape analysis | Posture prediction | Raster stereography | Symmetry line

Abstract: In a previous paper (Di Angelo, L., Di Stefano, P. and Morabito, A., 2011. Automatic evaluation of form errors in high-density acquired surfaces. International Journal of Production Research, 49 (7), 2061-2082) we proposed an original methodology for the automation of the geometric inspection, starting from an acquired high-density surface. That approach performed a recognition process on the acquired data aiming at the identification of some intrinsic nominal references. An intrinsic nominal reference was detected when a geometric property was recognised to be common to a set of adjacent points in the 3D data set representing the acquired object. The recognition of these properties was carried out based on some rules. Starting from these concepts, a new specification language was defined, which is based on recognisable geometric entities. This paper expands the category of intrinsic nominal references to include new mutual intrinsic orientation, location and dimensional properties pertaining to 3D features. This approach involves the automatic construction of a geometric reference model for a scanned workpiece, called recognised geometric model (RGM). The domain of the representable entities within the RGM strictly depends on the rules used for the recognition of the intrinsic properties. In particular, this paper focuses on the rules for the recognition of the orientation and location properties between non-ideal features. When using the RGM, tolerances are specified according to the set of available and recognisable intrinsic nominal references. Based on the geometric product specification, the RGM data structure can be queried to capture some quantitative information concerning special intrinsic geometric parameters and/or non-idealities. © 2012 Copyright Taylor and Francis Group, LLC.

Keywords: automated inspection | ISO tolerancing | shape recognition | three dimensional metrology | triangular meshes

Abstract: A correct prediction of build time is essential to calculate the accurate cost of a layer manufactured object. The methods presented in literature are of two types: detailed-analysis- and parametric-based approaches. The former require that a lot of data, related to the kinematic and dynamic performance of the machine, should be known. Parametric models, on the other hand, are of general use and relatively simple to implement; however, the parametric methods presented in literature only provide a few of the components of the total build time. Therefore, their performances are not properly suited in any case. In order to overcome these limitations, this paper proposes a parametric approach which uses a more complete set of build-time driving factors. Furthermore, considering the complexity of the parametric build time function, an artificial neural network is used so as to improve the method flexibility. The analysis of the test cases shows that the proposed approach provides a quite accurate estimation of build time even in critical cases and when supports are required. © 2011 Springer-Verlag London Limited.

Keywords: Artificial neural network | Build-time estimation | Rapid prototyping

Abstract: In this work a new method for symmetry line recognition, from 3D scanned data of a subject's back, is presented. The new method is validated by comparison with traditional techniques based on cutaneous marking. For this purpose, the upright standing and sitting postures of a sample of 75 subjects, who usually perform different sports activities, are analysed. Error in symmetry line detection is measured as the distance between the estimated symmetry line and the position of the markers. The proposed method is compared with another one described in literature which has been validated in clinical field. Results are analysed and critically discussed. © 2011 CAD Solutions, LLC.

Keywords: Back shape analysis | Posture prediction | Symmetry line

Abstract: This paper deals with the investigation of the stability and the accuracy of the most important methods to estimate the parameters that are involved in the shape recognition process of tessellated surfaces. For this purpose, four approaches to estimate the differential geometric properties of tessellated surfaces are systematically examined (namely, simple and extended quadric fitting methods, Rusinkiewicz's method and Meyer discrete method). A set of test cases has been designed in order to investigate the sensitivity of those methods to factors such as noise in point location, surface typology (chosen between those types that usually define the boundary of mechanical parts such as: planes, cylinders, spheres, cones and tori), mesh resolution and mesh regularity. Based on the results obtained, some criticism of the analyzed methods is made and some guidelines are provided in order to choose the most robust and reliable method in relation to the surface typology, quality of the mesh and noise in point location. © 2011 CAD Solutions, LLC.

Keywords: Curvature estimation | Shape recognition | Triangular meshes

Abstract: This paper presents a new high-performance method for triangular mesh generation based on a mesh-growing approach. Starting from a seed triangle, the algorithm grows the triangular mesh by selecting a new point based on the Gabriel 2Simplex criterion. This criterion can be considered to be a good approximation of the 2D Delaunay if the point cloud is well-sampled and not too rough. The performance of the proposed method is compared with that of the Cocone family and that of Ball Pivoting as regards the tessellation rate and the quality of the surface being generated from some benchmark point clouds and artificially noised test cases. The results are analysed and critically discussed. © 2011 Elsevier Ltd. All rights reserved.

Keywords: Reverse engineering | Surface reconstruction | Triangular meshes

Abstract: In this paper the authors present an original methodology aiming at the automation of the geometric inspection, starting from a high-density acquired surface. The concept of intrinsic nominal reference is herein introduced in order to evaluate geometric errors. Starting from these concepts, a new specification language, which is based on recognisable geometric entities, is defined. This work also proposes some surface differential properties, such as the intrinsic nominal references, from which new categories of form errors can be introduced. Well-defined rules are then necessary for the unambiguous identification of these intrinsic nominal references. These rules are an integral part of the tolerance specification. This new approach requires that a recognition process be performed on the acquired model so as to automatically identify the already-mentioned intrinsic nominal references. The assessable errors refer to recognisable geometric entities and their evaluation leaves the nominal reference specification aside since they can be intrinsically associated with a recognised geometric shape. Tolerance specification is defined based on the error categories which can be automatically evaluated and which are an integral part of the specification language. © 2011 Taylor & Francis.

Keywords: automated inspection | form error evaluation | GPS tolerancing

Abstract: The identification of C1 continuities is important in many applications involving point clouds or triangular meshes, such as surface segmentation, inspection and rendering. The methods in literature have some limitations which make them strongly dependent on some properties of the mesh (point typology, mesh resolution, uniformity of the shape of triangles and error in point location). Furthermore, some of them do not discriminate non-regular points from those that are inside a band around them. In this work, a new method for automatic detection of C1 continuities in triangular meshes is presented. The method introduces an original function, called sharpness indicator, which enables us to evaluate properties related to surface smoothness. The performance of the new method is compared with that of four methods presented in literature as regards the recognition of C1 continuities both in synthetic and real meshes. Results are analysed and critically discussed. © 2010 Elsevier Ltd. All rights reserved.

Keywords: C continuities detection 1 | Reverse engineering | Triangular meshes

Abstract: In this work a new method for symmetry line recognition, from 3D scanned data of a subject’s back, is presented. The new method is validated by comparison with traditional techniques based on cutaneous marking. For this purpose, the upright standing and sitting postures of a sample of 75 subjects, who usually perform different sports activities, are analysed. Error in symmetry line detection is measured as the distance between the estimated symmetry line and the position of the markers. The proposed method is compared with another one described in literature which has been validated in clinical field. Results are analysed and critically discussed. © 2010 Taylor & Francis Group, LLC.

Keywords: Back shape analysis | Posture prediction | Symmetry line

Abstract: Web-based e-commerce of rapid prototyping services is going to be a widely diffused methodology used to compete in a global market. A competitive market imposes a very accurate estimation of prototyping price. Prototype costs depend on many factors, some of which may be easily deduced, while some others consist in a complex function of the geometric model properties and of the specific technology employed to build a physical model. Build time, which affects some components of the prototype's build cost, is a critical factor to deduce. Build time depends not only on the prototype dimensions but also on the complexity of the shape that, in turn, affects the movement of the tool to form the object. A parametric approach to build cost estimation, suited for web-based e-commerce, is presented in this paper. Significant cost driving factors of layer manufactured objects are identified and instruments to evaluate them are proposed. Special attention has been paid to define a parametric approach to build time estimation. The proposed parametric approach analyses the geometrical features, which typically affect the build time of the main layer manufacturing technologies. The method is verified in some test cases related to FDM technology. © 2010 Taylor & Francis.

Keywords: Cost estimating | E-commerce | Rapid prototyping

Abstract: In this paper a statistical method for tolerances analysis and cost evaluation is presented. Statistical tolerances analysis is performed by assuming the Chase and Greenwood mean shift model, providing an original systematic approach to evaluate the mean shift factor. The proposed approach allows for the analysis of manufacturing costs for different confidence levels of the variables to be optimised. The interaction between customer requirements, design parameters and process variables, are taken into account by incorporating the process planning models and conceptual and embodiment design solutions. The cost analysis is performed by selecting the most appropriate driver for each component of the cost due tolerances. Cost driver parameters are evaluated over product life cycle, in different design domains (customer, design and process) and also include the customer satisfaction (quality loss).

Keywords: Cost analysis | Mean shift model | Tolerance analysis

Abstract: This paper describes a method for the recognition of the semantics of parts (features) of a component from a pure geometric representation. It is suitable for verifying product life-cycle requirements from the early stages of the design process. The proposed method is appropriate to analyse B-rep geometric models, and it is not limited to models described by planar and cylindrical surfaces, but it can handle several types of face shapes. In this work the concept of semanteme is introduced. A semanteme represents the minimal element of engineering meaning that can be recognised in a geometric model. The semantemes recognised in a part of the model, which are potentially of engineering significance, are used to associate an engineering meaning to the part. This approach gives a wide flexibility to the proposed system, which is suitable to be used in different contexts of application, since it is possible to describe the reference context using the semanteme that the system can manage. In the paper the implemented prototype system is briefly described. The prototype system takes advantage of neutral interfaces that allow geometrical and topological information to be retrieved from a commercial CAD system. © 2003 Elsevier Ltd. All rights reserved.

Keywords: Feature recognition | Intermediate geometric model | Semantics recognition

Abstract: The presence of fillets, rounds, chamfers and grooves is typical of many real-world mechanical components. Such features introduces in the model various topological and geometrical modifications which may alter the correct understanding of its main features. Another drawback which hinders the correct engineering evaluation of a part is that its geometrical and topological representation is not unique, since it depends either on the different procedures used to generate CAD models or on the different internal representation of the geometric kernels used by CAD packages. The overall aim of this work is to define an intermediate representation scheme which incorporates information about minor features such as chamfers, fillets, rounds and grooves into a graph based representation and overcomes the problem of non-uniqueness in the geometric representation. The representation scheme discussed here takes as input a solid model in B-rep form, and provides a description of a part at an higher level of abstraction in comparison with the raw B-rep description. A procedure for secondary features recognition is also described in this paper. The proposed algorithm consists of two steps where both topological/geometrical properties and dimensional attributes are investigated in order to fulfil a correct recognition. The recognized secondary features are then inserted into the model as labels which qualify the relationships between the faces of the graph representation. The resulting modelling scheme can be conveniently used for primary feature recognition as well as for other engineering analysis/simulation purposes. © 2003 IEEE.

Abstract: A geometric primitive for CAD implementation is presented in this paper (Bèzier Neural Network BNN). It is specifically designed to reproduce geometric shapes with functional requirements such as aerodynamic and hydrodynamic profiles. This primitive can be useful when a known and well defined map between functional requirements and geometric data does not exist, and it have to be deduced by a physical or numerical experimental analysis. BNN gives rise to a typical CAD representation, a Bèzier curve, of a functional profile, once the functional parameters are supplied. In BNN the capability of neural network to approximate very complex and non-linear function has been combined with the capability of Bèzier functions to describe geometry, in a unique neural network. In this work BNN is used in the representation of aerodynamic profiles starting to their typical functional parameters: lift and drag coefficients, Reynolds number and angle of attack. BNN is tested in reproducing the wing profile of the 4-digit NACA series. The output of BNN is compared with the results of a fluiddynamic analysis performed by commercial software. © 2003 IEEE.

Abstract: Tolerance design plays an important role in the modern design process by introducing quality improvements and limiting manufacturing costs. In this paper a method for statistical tolerance analysis and synthesis is presented. This method is implemented using the mean shift model of Chase and Greenwood, providing a systematic approach to evaluate the mean shift model method considers all the principal factors that affect the statistical sum of a certain number of assembly dimensions. In particular, the considered factors include the mean shift ratio, the confidence level, the number of dimension of the assembly and the tolerance assortment between the component dimensions. An implementation of the mean shift model for tolerance synthesis is described. The tolerances synthesis is performed in an unusual way, taking into account in the optimization process the typical parameters that affect the product variability. For this purpose the method uses four types of condition for the dimensional tolerances: fixed tolerance value, fixed mean shift ratio, fixed mean shift and fixed natural variability. Furthermore, in the optimization process, the service variability is considered under two conditions: fixed and valuable service variability. A case study is presented and the results of some simulations are discussed.

Keywords: Mean shift model | Tolerance analysis and synthesis

Abstract: This paper details a new method for automatic feature extraction from a Boundary Representation of the solid model. The proposed method is based principally on the evaluation of two topological invariants of concave parts of the modeled object. The result is a decomposition of the object boundary into surface components which represent shape features. Some aspects of the topology of bordered surfaces are discussed. The feature extraction method has been optimized for automatic core pattern design and advice in casting design. The main aspects of the "domain of application" of the method are considered, and six categories of shape features identified. The extraction rules proposed for a specific domain of application could be extended in different feature recognition contexts. © 1997 Elsevier Science Ltd.

Keywords: Feature recognition | Mold design

Abstract: The errors in the kinematic parameters of robots, due to the machining and to the assembly of the mechanical links, affect the positioning accuracy of robots. To obtain good accuracy these errors must be limited. In order to limit the positioning error it is important to carefully choose dimensional tolerances. Thus to obtain an optimum design of robots it is important to relate the positioning accuracy to the design tolerances, and then to manufacturing cost. This paper presents a method to synthesize the design tolerances of spatial robots, using a parameter that settles a relation between the cost and the positioning error. This method was implemented and tested on the Delta robot. Delta is a four degrees of freedom (dof) robot with a parallel structure, conceived for the manipulation of lightweight objects at fast working rhythms. After a statistical analysis of the effects of manufacturing tolerances and of the angular position of drives on the position accuracy, the method was applied obtaining optimal design and assembly tolerances to reach an assigned positioning accuracy.