3D scanning

This paper is devoted to the design and implementation of a novel moiré-based optical head mounted on the robotic arm of a coordinate measuring machine. The optical components of the recently developed two-projector moiré setup were miniaturized and integrated in the optical head. Special care was taken in minimizing the weight of the resulting structure so as to reduce as much as possible the forces acting on the robotic arm. The prototype of the optical head was tested by contouring the shape of different objects and measuring the displacements of a metallic bar subjected to compression loading. Measurements conducted with the proposed optical head were consistent with those obtained via a coordinate measuring machine (CMM). The values of the dimensions found fell always within the average ± standard deviation interval measured with the CMM. The optical head appears very suited for contouring the shape of objects and for determining the out-of-plane displacement field of mechanical components subjected to specific boundary and loading conditions. Furthermore, the system can be easily implemented inline in an industrial context to perform measurements as a product is being manufactured.

Keywords: Contouring , Coordinate measuring machine (CMM) , Optical scanning head , Projection moiré , Reverse engineering

The production of prostheses is still not completely optimized, especially for those districts where both functional and aesthetic requirements have to be combined with the urgency of intervention. The prostheses manufactured by machining using CAD/CAM techniques represent the conventional way to obtain a "custom-made" part. However, the above-mentioned solutions are penalized by the too long manufacturing time. This limit can be overcome by using an innovative metal-forming process, i.e. the Incremental Sheet Forming (ISF), which also allows to obtain complex patient-specific geometries even if characterized by a lower precision compared to the conventional process. In this paper, alternative approaches to manufacture a skull prosthesis (i.e. conventional milling and ISF) are compared from technological and economical points of view.

Keywords: Anchoring system design , Prostheses modelling , Skull manufacturing

This paper presents some experimentations, which have been conducted in the submerged archeological Park of Baiae, aimed to identify the problems related to the underwater 3D documentation process. The first test has been addressed to verify if a dense stereo mapping technique, usually employed in terrestrial and aerial applications, might be employed in critical underwater conditions by assessing the influence of different factors on the results. In the second test, the accuracy of the 3D model obtained through this technique has been evaluated. The third test deals with the geo-localization of the 3D models, conducted by merging the optical and acoustic data, through a multi-resolution bathymetric map of the site as a reference.

Keywords: 3D documentation , 3D model accuracy , 3D reconstruction , Baiae archeological park , Optical and acoustic data merging

Recovering correct or at least realistic colors of underwater scenes is a very challenging issue for imaging techniques, since illumination conditions in a refractive and turbid medium as the sea are seriously altered. The need to correct colors of underwater images or videos is an important task required in all image-based applications like 3D imaging, navigation, documentation, etc. Many imaging enhancement methods have been proposed in literature for these purposes. The advantage of these methods is that they do not require the knowledge of the medium physical parameters while some image adjustments can be performed manually (as histogram stretching) or automatically by algorithms based on some criteria as suggested from computational color constancy methods. One of the most popular criterion is based on gray-world hypothesis, which assumes that the average of the captured image should be gray. An interesting application of this assumption is performed in the Ruderman opponent color space lαβ, used in a previous work for hue correction of images captured under colored light sources, which allows to separate the luminance component of the scene from its chromatic components. In this work, we present the first proposal for color correction of underwater images by using lαβ color space. In particular, the chromatic components are changed moving their distributions around the white point (white balancing) and histogram cutoff and stretching of the luminance component is performed to improve image contrast. The experimental results demonstrate the effectiveness of this method under gray-world assumption and supposing uniform illumination of the scene. Moreover, due to its low computational cost it is suitable for real-time implementation.

Keywords: Color correction , Computational color constancy , Ruderman space , Underwater imaging

Main target of this paper is to analyse the advantages in the use of the Direct Modeling in the Virtual Prototyping processes and in the multiphysics analyses with the help of Reverse Engineering procedures. It is a recent CAD technique that allows the creation and/or modification of models that don't need parameters and constraints, as on the contrary happens in the Feature Based Modeling. So, it is possible to change the shapes and the dimensions of the original prototypes very easily. Hence, in this paper a methodology devised to acquire and modify a “reconstructed” (non-parametric) model to improve and then to submit it to FEM analysis is presented. Furthermore, it is realized and doesn't even need the Feature Recognition phase of a typical Reverse Engineering process. In particular, this methodology was applied to a frame of a bicycle used as case study. Its shape was acquired by means of a laser scanner and its virtual prototype was “reconstructed”. In addition, starting from it, two alternative frames were obtained and then easily modified by means of the Direct Modeling techniques. Then, they were submitted to FEM analyses to get different solutions with less weight but similar mechanical performances. Afterwards, the ergonomics of the modified configurations was tested by means of different percentile virtual manikins to plan the physical prototyping of a new improved bicycle.

Keywords: Bicycle , CATIA manikin , DELMIA simulations , Direct modeling , Feature based modeling , Feature recognition , FEM analysis , Reverse engineering

First target of this paper is to describe the design the behaviour of the final prototype before its manufacturing of an automotive semi-active differential based on the use of a and to predict its good performances and possible Magnetorheological Fluid (MRF). The MRF allows to control weaknesses. So the costs and the time to market of the new the locking torque and, consequently, to improve the vehicle handling. Second target is to propose a method grounded on a Close-Range Photogrammetry approach for the CAD modeling phase of the device ideated, alternative to the use of the typical Reverse Engineering (RE) techniques. In fact, although a Reverse Engineering process allows the complete 3D reconstruction of the external surfaces and features of a real object, it could often take a lot of time and, in some cases, could be affected by some approximations or errors. Furthermore, a model “reconstructed” could not be the best solution for multiphysics analyses, where the parametric geometry is needed for the modifications of all its features and dimensions for the optimization process in a very short time. For these reasons, in the case studied, the complete CAD prototype, created step by step, is needed and the photogrammetry can represent an interesting solution to enhance the virtual prototyping phase without repercussions on the quality of the results. Starting from the acquisition of particular “key points”, with an acceptable tolerance, the definition of the references (datum axes, curves, planes, centres of holes) needed for the CAD modeling, according to the Top-Down procedure, was possible. Once obtained the preliminary prototype, the final CAD model was created optimizing its dimensions and choosing the adequate materials. To evaluate the goodness of the procedure adopted, the MRF LSD geometry was reconstructed also by means of the Reverse Engineering techniques applied to the physical prototype of the new device ad hoc created. In particular, laser system acquisition and RE dedicated software were used. In this way the comparison between the photogrammetric and Reverse Engineering procedures (in terms of time spent and quality of the results) was allowed and so conducted. Lastly, the results of the FEM analyses carried out to validate the design process and the methodology ideated and adopted were showed.

Keywords: 3D CAD parametric modeling , Automotive differential , Direct modeling , FEM analysis , Magnetorheological fluid , Photogrammetry , Reverse engineering

This paper presents an applicative method for evaluating the global axis deformation of a sweep object caused by the manufacturing process with respect to its ideal CAD model. Object and CAD shapes are given in form of point clouds, the former derived from a laser-scanning measurement, the latter from sampling the original surface by a dense and uniform point grid. After an initial rigid registration, approximated centroidal axes of both shapes are extracted, compared and processed in order to evaluate macroscopical translation errors occurring in any scanned object's section. This method has been applied and tested to the analysis of a helical Darrieus blade prototype, parametrically designed and modelled with McNeel Rhinoceros and Grasshopper software, manufactured with a three-axes CNC machine and reinforced by a carbon fibre composite laminate. The point cloud obtained from the subsequent laser scanning has been processed and compared to the original NURBS model in order to build the global contour map of the mutual difference. The application of this procedure is able to check the conformity of the manufactured airfoil to the theoretical one and, therefore, to establish the efficiency of the final prototype of the blade turbine.

Keywords: axis deformation , error estimation , Point Cloud

Seagrass meadows are complex ecosystems representing an important source of biodiversity for coastal marine systems, but are subjected to numerous threats from natural and human-based influences. Due to their susceptibility to changing environmental conditions, seagrasses are habitually used in monitoring programmes as biological indicators to assess the ecological status of coastal environments. In this paper we used a non-destructive photo mosaicing technology to quantify seagrass distribution and abundance, and explore benefits of micro-cartographic analysis. Furthermore, the use of photogrammetric tools enhanced the method, which proved to be efficient due to its use of low-cost instruments and its simplicity of implementation. This paper describes the steps required to use this method in meadows of Posidonia oceanica, including: i) camera calibration procedures, ii) programming of video survey, iii) criteria to perform sampling activities, iv) data processing and micro-georeferenced maps restitution, and v) possible study applications.

Keywords: Mapping , Photo mosaicing , Photogrammetry , Posidonia oceanica , Seagrass , Underwater photography

Seagrass communities are considered one of the most productive and complex marine ecosystems. Seagrasses belong to a small group of 66 species that can form extensive meadows in all coastal areas of our planet. Posidonia oceanica beds are the most characteristic ecosystem of the Mediterranean Sea, and should be constantly monitored, preserved and maintained, as specified by EU Habitats Directive for priority habitats. Underwater 3D imaging by means of still or video cameras can allow a detailed analysis of the temporal evolution of these meadows, but also of the seafloor morphology and integrity. Video-photographic devices and open source software for acquiring and managing 3D optical data rapidly became more and more effective and economically viable, making underwater 3D mapping an easier task to carry out. 3D reconstruction of the underwater scene can be obtained with photogrammetric techniques that require just one or more digital cameras, also in stereo configuration. In this work we present the preliminary results of a pilot 3D mapping project applied to the P. oceanica meadow in the Marine Protected Area of Capo Rizzuto (KR, Calabria Region-Italy).

Keywords: 3D mapping , 3D reconstruction , Optical instruments , Posidonia oceanica , Quality status

Documentation of maritime heritage is essential for its protection, and for reference in restoration and renovation processes. These functions become problematic in the case of historical ships and boats that lack lines drawings. The purpose of this paper is to describe a procedure for creation of lines drawings based on the shape analysis of surviving historical boats or their small-scale models with the help of reverse engineering (RE) techniques. The paper describes how digital photogrammetry and the iterative method were used to analyze the shape of three historical boats: Tomahawk, Refola and Nada. The application of the proposed procedure produced the lines drawings of the boats as its result. The accuracy of the 3D CAD model obtained with the photogrammetric technique was verified by comparing it against a more accurate 3D model produced with the help of a RE laser scanner. The examination of the resulting lines drawings proves that the digital photogrammetry process and the proposed iterative method are adequate tools for developing lines plans of boat models. The research offers the methodological basis for the creation of an archive of lines drawings of historical boats. Such an archive would provide reference for philologically correct restorations, and permit definition and classification of distinctive elements of various types of historical boats, particularly those produced in the Campania Region. © 2014 Springer Science+Business Media New York.

Keywords: 3D CAD models , Digital photogrammetry , Laser scanning , Maritime heritage documentation , Philological reconstruction , Reverse engineering

Aim Today Cone Beam Computed Tomography (CBCT) has become an important image technique for dento-maxilla facial applications. In the paper a new method to assess the geometric accuracy of these systems was proposed. It uses a free form benchmark model and a non-contact Reverse Engineering (RE) system. Method The test geometry chosen for this study was designed in such a way that it simulated human spongy bone, cortical bone, gingiva and teeth and it composed of removable free form parts. It was acquired with a high-resolution laser scanner (D700 Scanner - 3Shape, Denmark). The reference 3D surface models obtained with the laser scanner was compared with the 3D models that were created from a CBCT system (Scanora 3D - Soderex, Finland) and from a traditional Multi-Slice Computed Tomography (MSCT) scanner (LightSpeed VCT 64 Slice - General Electric, USA) at different reconstruction settings, using an iterative closest point algorithm (ICP) in Geomagic® software. Results The comparison between the different pairs of CAD models clearly shows that there is a good overlap between the models. Conclusions Although the results obtained in this study could lead to increase the use of CBCT for an increasing number of dental procedures, the publication of the European Commission guidelines represents a baseline on which the clinicians should rely heavily when considering the use of CBCT in their practice. Clinical Significance The results of this research show that the accuracy of CBCT 3D models is comparable to MSCT 3D models. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Benchmark free form model , Cone Beam Computed Tomography (CBCT) , Laser scan , Multi-Slice Computed Tomography (MSCT) , Virtual modelling

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

This paper describes a research activity concerning the design and the development of an automotive semi-active differential based on the use of a magnetorheological fluid that allows to control the locking torque and, consequently, to improve the vehicle handling. Starting from a gearbox of a common front wheel drive vehicle, the boundary volume of the new device was defined by means of reverse engineering techniques. Two alternative architectures were proposed and compared to select the best one in terms of functionality. Then, the selected functional scheme was modeled and optimized by means of multiphysics simulations. The definition of a reiterative process, based on the use of a specific cost function, allowed to optimize the design variables and to obtain the final virtual prototype. In order to evaluate the effectiveness of the proposed device, a physical prototype was realized. First experimental tests were carried out validating the design process. © 2014 Elsevier Ltd. All rights reserved.

Keywords: Automotive differential , Mechatronic device , Optimal design , Reverse engineering , Virtual prototyping techniques

The accurate reconstruction of a human digital dental model represents a wide research area within the orthodontic field due to its importance for the customization of patient treatments. Usually, 3-D dental root geometries are obtained by segmenting tomographic data. However, concerns about radiation doses may be raised since tomographic scans produce a greater X-ray dose than conventional 2-D panoramic radiographs (PAN). The present work is aimed at investigating the possibility to retrieve 3-D shape of individual teeth by exposing the patient to the minimum radiation dose. The proposed methodology is based on adapting general CAD templates over patient-specific dental anatomy, which is reconstructed by integrating the optical digitization of dental plaster models with a PAN image. The radiographic capturing process is simulated through the Discrete Radon Transform (DRT) and performed onto the patient crowns geometry obtained by segmenting the digital plaster model. A synthetic PAN image is then reconstructed and used to integrate the radiographic data within the digitized plaster model, thus allowing to retrieve roots information which guide the CAD templates adapting over the patient anatomy.

In the aerospace sector, tolerance allocation and inspection of many components must provide not only for ease of manufacturing and cost reduction but also for reliability and safety requirements. Computer Aided Tolerancing and Inspection (CAT&I) methods based on Reverse Engineering techniques may enhance production quality assessment with significant reduction of the time-to-market. This paper presents an original reverse engineering methodology that is being developed to achieve the complete automation of the inspection process starting from the design requirements (dimensional and geometrical tolerances) as they generally appear in the component's official drawings. After a brief presentation of the proposed methodology and its possible implementation oriented to non-planar surface recognition, an aeronautical component made by beta-forging of Ti6Al4V Titanium Alloy powders is presented as test case. The discussion of the procedure allows to point out its benefits in terms of (a) more efficient management of the inspection process and data consolidation; (b) more thorough comprehension of the real component; and (c) a better understanding of possible feedbacks to be applied in design or manufacturing. Finally some remarks about the limits of the proposed methodology are shown and possible enhancements, that have been already planned to be applied, will be described. © 2014 IEEE.

Keywords: beta-forging , Computer Aided Tolerancing and Inspection , Reverse Engineering , Segmentation , Ti6Al4V Titanium Alloy powders

ABSTRACT: This paper presents a point cloud segmentation based on a spatial multiresolution discretisation that is derived from hierarchical space partitioning. Through part type recognition it aims to simplify Computer Aided Tolerance Inspection of electromechanical components avoiding cloud-CAD model registration. A voxel structure subdivides the point cloud. Then, through a suitable surface partitioning, it is linked to component volumes by means of the morphological components of the binary image that is derived from voxel attributes (‘true state' if points are included in a specific cluster or ‘false state' if they are not). The proposed approach is then applied on a din-rail clip of a breaker, made by injection moulding. This case study points out the suitability of the approach on box-shaped components or with normal protrusions, and its limits concerning the assumptions of the implementation.

Keywords: computer aided tolerance inspection , reverse engineering , segmentation

Designing physical interfaces, like the doors of consumer products, able to elicit a positive experience when interacting with them, is now becoming a key priority for design teams. One of the main difficulties of this activity consists of translating all the qualitative perceptual feedback that can be captured from the customers into quantitative specifications. Performing this translation is not an easy task since there are still no effective tools, methodologies or approaches able to guide designers in accomplishing this goal. To overcome this lack a reverse engineering-based approach is proposed. This one guides designers towards the modelling, parameterisation and reproduction of the behaviour of the product interface to be redesigned, within a multisensory virtual environment. The intent is to let the user experience different behaviours in order to ask them to identify the desired one or to express preferences for updating it in real-time according to indications provided. At the same time a detailed physics model, built by the designer, is used to convert this desired behaviour, into detailed quantitative design specifications. The method is defined as a reverse engineering one for two main reasons: first the new interaction is derived on the basis of the behaviour of an existing interface, taken as reference, and second a reverse engineering of the user's perceptual preferences is applied to derive new specifications. A case study is discussed to demonstrate the method effectiveness and to highlight its limitations. © 2014 Taylor & Francis.

Keywords: haptics , interactive systems , product experience , reverse engineering , virtual prototyping

The application of three-dimensional (3D) facial analysis and landmarking algorithms in the field of maxillofacial surgery and other medical applications, such as diagnosis of diseases by facial anomalies and dysmorphism, has gained a lot of attention. In a previous work, we used a geometric approach to automatically extract some 3D facial key points, called landmarks, working in the differential geometry domain, through the coefficients of fundamental forms, principal curvatures, mean and Gaussian curvatures, derivatives, shape and curvedness indexes, and tangent map. In this article we describe the extension of our previous landmarking algorithm, which is now able to extract eyebrows and mouth landmarks using both old and new meshes. The algorithm has been tested on our face database and on the public Bosphorus 3D database. We chose to work on the mouth and eyebrows as a separate study because of the role that these parts play in facial expressions. In fact, since the mouth is the part of the face that moves the most and affects mainly facial expressions, extracting mouth landmarks from various facial poses means that the newly developed algorithm is pose-independent.

Keywords: 3D face , 3D scanner , Differential geometry , Face morphology , Medical diagnosis , Soft-tissue landmarks

The face is perhaps the most important human anatomical part, and its study is very important in many fields, such as the medical one and the identification one. Technical literature presents many works on this topic involving bi-dimensional solutions. Even if these solutions are able to provide interesting results, they are strongly subjected to images distortion. Thanks to the significant improvements obtained in the 3D scanner domain (photogrammetry for instance), today it is possible to replace the 2D images with more precise and complete 3D models (triangulated points clouds). Working on three-dimensional data, in fact, it is possible to obtain a more complete set of information about the face morphology. At present, even if it is possible to find interesting papers on this field, there is the lack of a complete protocol for converting the big amount of data coming from the three-dimensional point clouds in a reliable set of facial data, which could be employed for recognition and medical tasks. Starting from some anatomical human face concepts, it has been possible to understand that some soft-tissue landmarks could be the right data set for supporting many processes working on three-dimensional models. So, working in the Differential Geometry domain, through the Coefficients of the Fundamental Forms, the Principal Curvatures, Mean and Gaussian Curvatures and also with the derivatives and the Shape and Curvedness Indexes, the study has proposed a structured methodology for soft-tissue landmark formalization in order to provide a methodology for their automatic identification. The proposed methodology and its sensitivity have been tested with the involvement of a series of subjects acquired in different scenarios. © 2012 Springer Science+Business Media, LLC.

Keywords: 3D models , 3D scanners , Face morphology , Soft tissue landmarks

3D reconstructions of small objects are more and more frequently employed in several disciplines such as medicine, archaeology, restoration of cultural heritage, forensics, etc. The capability of performing accurate analyses directly on a three-dimensional surface allows for a significant improvement in the accuracy of the measurements, which are otherwise performed on 2D images acquired through a microscope. In this work we present a new methodology for the 3D reconstruction of small sized objects based on a multi-view passive stereo technique applied on a sequence of macro images. The resolving power of macro lenses makes them ideal for photogrammetric applications, but the very small depth of field is their biggest limit. Our approach solves this issue by using an image fusion algorithm to extend the depth of field of the images used in the photogrammetric process. The paper aims to overcome the problems related to the use of macro lenses in photogrammetry, showing how it is possible to retrieve the camera calibration parameters of the sharp images by using an open source Structure from Motion software. Our approach has been tested on two case studies, on objects with a bounding box diagonal ranging from 13.5. mm to 41. mm. The accuracy analysis, performed on certified gauge blocks, demonstrates that the experimental setup returns a 3D model with an accuracy that can reach the 0.05% of the bounding box diagonal. © 2013 Elsevier Masson SAS.

Keywords: 3D reconstruction , Cultural heritage , Digital documentation , Image fusion , Macro lens , Small objects