Wood fiber orientation assessment based on punctual laser beam excitation: A preliminary study

International audienceThe EU imposes standards for the use of wood in structural applications. Local singularities such as knots affect the wood mechanical properties. They can be revealed by looking at the wood fiber orientation. For this reason, many methods were proposed to estimate the orientation of wood fiber using optical means, X-rays, or scattering measurement techniques. In this paper, an approach to assess the wood fiber orientation based on thermal ellipsometry is developed. The wood part is punctually heated with a Nd-YAG Laser and the thermal response is acquired by an infrared camera. The thermal response is elliptical due to the propagation of the heat through and along the wood fibers. An experiment is presented to show the capacity of such techniques to assess fiber orientation on wood specimen. In addition, an appropriate algorithm is given to extract the orientation of the ellipse

OCM 2021 - Optical Characterization of Materials

The state of the art in the optical characterization of materials is advancing rapidly. New insights have been gained into the theoretical foundations of this research and exciting developments have been made in practice, driven by new applications and innovative sensor technologies that are constantly evolving. The great success of past conferences proves the necessity of a platform for presentation, discussion and evaluation of the latest research results in this interdisciplinary field

OCM 2021 - Optical Characterization of Materials : Conference Proceedings

The state of the art in the optical characterization of materials is advancing rapidly. New insights have been gained into the theoretical foundations of this research and exciting developments have been made in practice, driven by new applications and innovative sensor technologies that are constantly evolving. The great success of past conferences proves the necessity of a platform for presentation, discussion and evaluation of the latest research results in this interdisciplinary field

Material Recognition Meets 3D Reconstruction : Novel Tools for Efficient, Automatic Acquisition Systems

For decades, the accurate acquisition of geometry and reflectance properties has represented one of the major objectives in computer vision and computer graphics with many applications in industry, entertainment and cultural heritage. Reproducing even the finest details of surface geometry and surface reflectance has become a ubiquitous prerequisite in visual prototyping, advertisement or digital preservation of objects. However, today's acquisition methods are typically designed for only a rather small range of material types. Furthermore, there is still a lack of accurate reconstruction methods for objects with a more complex surface reflectance behavior beyond diffuse reflectance. In addition to accurate acquisition techniques, the demand for creating large quantities of digital contents also pushes the focus towards fully automatic and highly efficient solutions that allow for masses of objects to be acquired as fast as possible. This thesis is dedicated to the investigation of basic components that allow an efficient, automatic acquisition process. We argue that such an efficient, automatic acquisition can be realized when material recognition "meets" 3D reconstruction and we will demonstrate that reliably recognizing the materials of the considered object allows a more efficient geometry acquisition. Therefore, the main objectives of this thesis are given by the development of novel, robust geometry acquisition techniques for surface materials beyond diffuse surface reflectance, and the development of novel, robust techniques for material recognition. In the context of 3D geometry acquisition, we introduce an improvement of structured light systems, which are capable of robustly acquiring objects ranging from diffuse surface reflectance to even specular surface reflectance with a sufficient diffuse component. We demonstrate that the resolution of the reconstruction can be increased significantly for multi-camera, multi-projector structured light systems by using overlappings of patterns that have been projected under different projector poses. As the reconstructions obtained by applying such triangulation-based techniques still contain high-frequency noise due to inaccurately localized correspondences established for images acquired under different viewpoints, we furthermore introduce a novel geometry acquisition technique that complements the structured light system with additional photometric normals and results in significantly more accurate reconstructions. In addition, we also present a novel method to acquire the 3D shape of mirroring objects with complex surface geometry. The aforementioned investigations on 3D reconstruction are accompanied by the development of novel tools for reliable material recognition which can be used in an initial step to recognize the present surface materials and, hence, to efficiently select the subsequently applied appropriate acquisition techniques based on these classified materials. In the scope of this thesis, we therefore focus on material recognition for scenarios with controlled illumination as given in lab environments as well as scenarios with natural illumination that are given in photographs of typical daily life scenes. Finally, based on the techniques developed in this thesis, we provide novel concepts towards efficient, automatic acquisition systems

Reverse engineering of obsolete components for realisation using additive manufacturing

Additive manufacturing (AM), or 3D printing as it also known, is a technique used for the direct manufacture of parts, one which is becoming more accessible to not just engineers in industry, but also non-technical users with minimal technical knowledge or experience. The aim of the research was the investigation of the possibilities that AM presents for realising the manufacture of obsolete parts from older systems. Consideration of multiple AM techniques and their individual benefits and drawbacks is presented. To reverse engineer (RE) a part for additive manufacture requires the use of 3D modelling software packages as well as access to AM equipment to fully investigate how to best produce replacement parts. The thesis also considers various data creation and scanning technologies, used to digitise the geometry of parts, a key component in the RE process. The digitised component can then be manipulated in modelling software to provide the files required for AM. To replace components from older systems that are no longer in production can incur massive costs with respect to their manufacture using various moulds, machinery and tools. Using AM, it is shown that these costs could be greatly reduced, and material waste kept to an absolute minimum. With the incorporation of 3D modelling and simulation/analysis software, the mechanical performance of a component is also analysed. A component from an obsolete coffee roaster was subjected to the process of RE for replacement. The desktop AM machine used produced a part of sufficient quality to allow its use as a sandcasting pattern. By using AM instead of a traditional pattern, time savings and thus cost savings were achievable in the manufacturing process. A larger version of the component was scanned to create the 3D model from which the sandcasting pattern could be created. This was not successful as the 3D scanners could not produce a scan of satisfactory detail to work with. An investigation into the capabilities of the scanner was then carried out to determine if lower priced scanners are a worthwhile investment. This showed that while they are not ideal for 1:1 scaled replications of geometries, they are useful should a miniature version be required. It is recommended that scanners do not represent the same value for money in terms of quality produced that low end desktop AM machines do

3-D scanning of nonopaque objects by means of imaging emitted structured infrared patterns

Three-dimensional surface acquisition is a subject that has been studied to a large extent; a significant number of techniques for acquiring shapes have been proposed, and a wide range of commercial solutions is available. Nevertheless, today's systems still have difficulties when digitizing objects that are transparent or semitransparent in the visible range. In this paper, some of the issues of traditional scanning systems are addressed by considering the radiative properties of materials. As a result, an infrared laser light-based scanner is presented for successfully acquiring the shape of complex surfaces by analyzing heat patterns that are emitted by the object

Graduate School: Course Decriptions, 1972-73

Official publication of Cornell University V.64 1972/7

Reconstruction tridimensionnelle par stéréophotométrie

Cette thèse traite de la reconstruction 3D par stéréophotométrie, qui consiste à utiliser plusieurs photographies d'une scène prises sous le même angle, mais sous différents éclairages. Nous nous intéressons dans un premier temps à des techniques robustes pour l'estimation des normales à la surface, et pour leur intégration en une carte de profondeur. Nous étudions ensuite deux situations où le problème est mal posé : lorsque les éclairages sont inconnus, ou lorsque seuls deux éclairages sont utilisés. La troisième partie est consacrée à l'étude de modèles plus réalistes, à la fois en ce qui concerne les éclairages et la réflectance de la surface. Ces trois premières parties nous amènent aux limites de la formulation classique de la stéréophotométrie : nous introduisons finalement, dans la partie 4, une reformulation variationnelle et différentielle du problème qui permet de dépasser ces limites