Towards Skeleton based Reconstruction : From Projective Skeletonization to Canal Surface Estimation

International audienceWe present a novel approach to reconstruct a 3D object from images corresponding to two different viewpoints: we estimate the skeleton of the object instead of its surface. The originality of the method is to be able to reconstruct a tubular object with a limited number of input images. Unlike classical reconstruction methods, like multi-view stereo or more recently structure-from-motion, this approach does not rely on interest points but estimates the topology of the object and derives its surface. Our contribution are twofold. First, given two perspective images of the 3D shape, the projection of the skeleton is computed in 2D. Secondly the 3D skeleton is reconstructed from the two projections using triangulation and matching. A mesh is finally derived for each skeleton branch

Caractérisation de la projection du squelette d'une surface canal 3D : Application à la reconstruction 3D à partir de deux images

International audienceNous présentons dans cet article une nouvelle approche pour reconstruire un objet 3D à partir de deux images de celui-ci. L'originalité de notre approche vient du fait que nous n'estimons pas directement la surface de l'objet 3D mais son squelette. Ce travail s'appuie sur les deux contributions suivantes. Premièrement, nous décrivons la relation existant entre un squelette 3D et sa projection, orthographique ou perspective, sur un plan image. Ensuite, nous montrons comment retrouver le squelette 3D à partir de deux de ses projections. Contrairement aux méthodes de reconstruction 3D classiques qui génèrent un nuage de points sans maillage, cette approche a pour avantage de reconstruire aussi la topologie de l'objet, c'est-à-dire d'en retrouver un maillage sans traitement annexe. Nous traitons ici des objets représentables par un squelette 3D curviligne et nous supposons aussi que les points de vue sont calibrés

Image registration algorithm for molecular tagging velocimetry applied to unsteady flow in Hele-Shaw cell

In order to develop velocimetry methods for confined geometries, we propose to combine image registration and volumetric reconstruction from a monocular video of the draining of a Hele-Shaw cell filled with water. The cell’s thickness is small compared to the other two dimensions (e.g. 1x400 x 800 mm3). We use a technique known as molecular tagging which consists in marking by photobleaching a pattern in the fluid and then tracking its deformations. The evolution of the pattern is filmed with a camera whose principal axis coincides with the cell’s gap. The velocity of the fluid along this direction is not constant. Consequently, tracking the pattern cannot be achieved with classical methods because what is observed is the integral of the marked molecules over the entire cell’s gap. The proposed approach is built on top of direct image registration that we extend to specifically model the volumetric image formation. It allows us to accurately measure the motion and the velocity profiles for the entire volume (including the cell’s gap) which is something usually hard to achieve. The results we obtained are consistent with the theoretical hydrodynamic behaviour for this flow which is known as the Poiseuille flow

Micro computed tomography based finite element models of calcium phosphate scaffolds for bone tissue engineering

Bone is a living tissue that is able to regenerate by itself. However, when severe bone defects occur, the natural regeneration may be impaired. In these cases, bone graft substitutes can be used to induce the natural healing process. As a scaffold for tissue engineering, these bone graft substitutes have to meet specific requirements. Among others, the material must be biocompatible, biodegradable and have a porous structure to allow vascularization, cell migration and formation of new bone. Additionally, the mechanical properties of the scaffold have to resemble the ones of native tissue. The goal of this project is to create a computational model of the calcium phosphate scaffolds that are produced by rapid-prototyping by the Biomaterials, Biomechanics, and Tissue Engineering group at the Technical University of Catalonia. These models are based on finite element analysis and micro computed tomography images in order to consider the actual architecture of the scaffolds. The generated FE-models allow the computation of both local strains, which act as mechanical stimuli on attached cells, as well as the behaviour of the entire scaffold. When considering this information, the scaffold can be optimized for tissue differentiation by tuning both the scaffold architecture and the scaffold material bulk properties.Incomin

THE VENETIAN GALEA: From the WOODEN MODEL to the DIGITAL MODEL

The Venetian galea (galley), dominating the Mediterranean Sea for almost 1000 years, is one of the most emblematic and fascinating objects in the history and culture of the Serenissima Republic of San Marco, the official name of ancient Venice. This boat has changed according to the needs and developments that have taken place over the centuries, proving versatile and powerful in military and commercial use. Unfortunately, no complete specimen has been received, and everything that can be known about galleys derives from paintings made in different eras, in models and in some original parts, kept inside the Naval Historical Museum of Venice. Another source are some manuscripts, where part of the traditional shipbuilding knowledge is handed down. To understand a galley it is necessary to understand which techniques were used by the proti (directors of the ancient shipyard) which differ substantially from the current design. These techniques were the synthesis of knowledge handed down from person to person and which did not make use of design drawings such as are used today. To obtain the reconstruction of a galley, lacking complete original drawings, we collected and analyzed different documentation that testified the ancient forms. The presented work aims to reconstruct a digital model of a galea starting from the photogrammetric and laser scanning survey of a wooden model of the hull of half of a 25-bench galley of the mid-seventeenth century. The surveyed maquette and brought back to the real scale was integrated by some artifacts present at the Naval History Museum of Venice, surveyed with photogrammetric techniques and laser scanning too. In this way a hypothetical configuration was reconstructed (by synthesis of collected and historical data) which shows the shape that this boat could reasonably have had. The result is a digital model, then printed to the scale, obtained by three-dimensional modeling starting from the point clouds of the maquette and the original artifacts. This final model has been compared with all the iconographic and documentary sources for its historical validation. The results obtained were used for a set-up aimed at enhancing the museum, because it was intended for a large audienc

Confocal Laser Scanning Microscopy As A Tool For The Investigation Of Tetracycline Fluorescence In Archaeologicalhuman Bone

Fluorochromes such as tetracycline have been used to label bone for histomorphometric analysis, measuring bone formation, growth, maintenance, and pathology. More recently, similar fluorescence has been observed in ancient human bone. Attributed to tetracycline (TC) exposure, this phenomenon could affect various aspects of health during life and/or preservation of remains postmortem. Standard epifluorescence microscopy is the most common tool employed in the analysis of these labels. Though valuable, this technique is limited by its inability to penetrate bone three-dimensionally and its inclusion of out-of-focus light, possibly disrupting accurate analysis. Confocal Laser Scanning Microscopy (CLSM) has been demonstrated as a valuable tool for three-dimensional histology. Its application to the study of compact bone fluorescence has been lacking, especially in archaeological and forensic sciences. In the following two papers, modern TC-controlled bone is compared to well preserved archaeological bone recovered from the Dakhleh Oasis, Egypt, using both standard wide-field and more modern confocal techniques for imaging and analysis. Spectral analysis via CLSM shows that both modern and ancient fluorescent labels in bone share the exact same fluorescence emission peak at 525 nm. Differences in the shape of the spectral curve and photobleaching characteristics are discussed. In addition, CLSM\u27s high-resolution two- and three-dimensional imaging capabilities (in polarized light, scattered light, and fluorescence light) are found to increase the flexibility and creativity of investigations into the occurrence of tetracycline labels in archaeological bone and could have added benefits for modern medical and anatomical experimentation