CALIBRATION OF 3D KINEMATIC SYSTEMS USING 2D CALIBRATION PLATE

3D kinematic systems based on the images acquired by cameras are one of the most popular tools for a human motion analyses. Prior to the actual reconstruction a camera calibration procedure is needed. Originally 3D calibration cages were utilized for that purpose, but nowadays a vast majority of commercial systems rely on the wand calibration. When the highest degree of accuracy is requested, than using 3D calibration cage is often recommended over the wand calibration. On the other hand, from a user point of view a wand calibration is generally regarded as the most user friendly. A substantial ‘intermediate’ solution would be using 2D calibration plate. Interestingly, there could be hardly found any trace that commercial 3D kinematic systems ever relied on 2D calibration plate. The purpose of this study was to investigate quantitative and qualitative aspects of calibrating the 3D kinematic system using 2D calibration plate

Razvoj biomedicinskog inženjerstva u Hrvatskoj

Biomedicinsko inženjerstvo značajno je doprinijelo promjenama u zdravstvenoj zaštiti i medicini, pa i ostalim biomedicinskim znanostima. Medi-cina i zdravstvena zaštita ovise o visokoj tehnologiji za prevenciju, dijagnosti-ku i liječenje bolesti, te za rehabilitaciju pacijenata. Biomedicinsko inženjer-stvo predstavlja jedno (od dvije) najbrže rastuće grane industrije u razvijenom svijetu, temeljeno na inovacijama što pokazuju statistike Europskog patentnog zavoda prema kojima je čitavo desetljeće broj patentnih prijava upravo najvi-še u području medicinske tehnologije. Razvoj biomedicinskog inženjerstva u Hrvatskoj započeo je institucionalno početkom sedamdesetih godina prošlog stoljeća, a nosioci razvoja bili su Elektrotehnički fakultet (danas Fakultet elektrotehnike i računarstva) i Fakultet strojarstva i brodogradnje Sveučilišta u Zagrebu. U ovom radu dan je prikaz dijela istraživačkih i inženjerskih do-stignuća njihovih istraživačkih timova u proteklim desetljećima

Mesure de formes par corrélation multi-images : application à l'inspection de pièces aéronautiques à l'aide d'un système multi-caméras

L'Ecole des Mines d'Albi et le LAAS-CNRS ont engagé en 2006 une collaboration avec AIRBUS Toulouse et EADS-IW pour le développement d'un système de vision artificielle destiné à l'inspection de pièces aéronautiques (panneaux de fuselage ou de voilure, métalliques ou composites) en vue de la détection de défauts de forme (écarts à la forme nominale souhaitée). Le système est constitué de plusieurs caméras (au moins quatre) afin de pouvoir inspecter des pièces de grande taille. Les caméras sont fixées sur une structure rigide statique et les pièces à inspecter sont positionnées devant cette structure. N images de la pièce à inspecter sont acquises de façon synchronisée et sont utilisées afin de reconstruire la pièce observée en 3D. Ce mémoire aborde les différentes stratégies envisagées pour l'exploitation d'un système multi-caméras. Les étapes nécessaires à la numérisation d'une pièce sont présentées, et plus particulièrement : l'appariement par corrélation multi-images (un critère de corrélation multi-images bien adapté au contexte multi-caméras est décrit), le recalage de nuages de points 3D par corrélation d'images, et l'aide au calibrage. L'utilisation de plusieurs caméras a montré de nombreux avantages. Elle permet la numérisation d'objets de grande taille (surface de plusieurs m²), fournit la forme complète d'un objet à partir d'une seule acquisition d'images (acquisition one-shot), améliore la précision de numérisation grâce à la redondance d'informations, permet de s'affranchir de problèmes de réflexion spéculaire dans le cas d'objets réfléchissants. Les algorithmes développés ont été évalués à la fois à partir d'images synthétiques et par comparaison aux mesures fournies par plusieurs systèmes commerciaux de numérisation 3D.In 2006 the Ecole des Mines d'Albi and the LAAS-CNRS initiated a collaboration with AIRBUS Toulouse and EADS-IW for the development of a computer-vision-based system for the inspection of aeronautic parts (fuselage parts, metallic or composite aeronautical panels, etc.) in order to detect shape defects (shape deviation with regard to the desired overall shape corresponding to the CAD model). The system is composed of several cameras (at least four) giving the capacity to inspect large parts. The cameras are fixed on a rigid structure and the parts to be inspected are positioned in front of the system. Several images are acquired synchronously and they are used to reconstruct the 3D model of the part. This thesis focuses on different strategies that can be developed to manage a multiple-camera system. The different steps of the digitization process are presented, namely: multiple-view digital image correlation (a multiple-image DIC criterion well suited to the multiple views context is addressed), 3D cloud stitching, calibration assistance unit. Using more than two cameras has brought multiple benefits. It allows digitizing large aeronautic parts (several m²), provides the whole shape of an object in a one-shot acquisition, improves the accuracy thanks to data redundancy, and permits to avoid specular reflections on non-lambertian surfaces. Our algorithms have been evaluated through synthetic images as well as through the comparison with measurements acquired by different commercial digitizing systems

Calibration of 3D kinematic systems using orthogonality constraints

International audienceProcessing images acquired by multi-camera systems is nowadays an effective and convenient way of performing 3D reconstruction. The basic output, i.e. the 3Dlocation of points, can easily be further processed to also acquire information about additional kinematic data: velocity and acceleration. Hence,many such reconstruction systems are referred to as 3D kinematic systems and are very broadly used, among other tasks, for human motion analysis. A prerequisite for the actual reconstruction of the unknown points is the calibration of the multi-camera system. At present, many popular 3D kinematic systems offer so-called wand calibration, using a rigid bar with attached markers, which is from the end user's point of view preferred over many traditional methods. During this work a brief criticism on different calibration strategies is given and typical calibration approaches for 3Dkinematic systems are explained. In addition, alternativeways of calibration are proposed, especially for the initialization stage. More specifically, the proposed methods rely not only on the enforcement of known distances between markers, but also on the orthogonality of two or three rigidly linked wands. Besides, the proposed ideas utilize common present calibration tools and shorten the typical calibration procedure. The obtained reconstruction accuracy is quite comparable with that obtained by commercial 3D kinematic systems

Machine Vision and Applications DOI 10.1007/s00138-007-0068-0 ORIGINAL PAPER Calibration of 3D kinematic systems using orthogonality constraints

Abstract Processing images acquired by multi-camera systems is nowadays an effective and convenient way of performing 3D reconstruction. The basic output, i.e. the 3D location of points, can easily be further processed to also acquire information about additional kinematic data: velocity and acceleration. Hence, many such reconstruction systems are referred to as 3D kinematic systems and are very broadly used, among other tasks, for human motion analysis. A prerequisite for the actual reconstruction of the unknown points is the calibration of the multi-camera system. At present, many popular 3D kinematic systems offer so-called wand calibration, using a rigid bar with attached markers, which is from the end user’s point of view preferred over many traditional methods. During this work a brief criticism on different calibration strategies is given and typical calibration approaches for 3D kinematic systems are explained. In addition, alternative ways of calibration are proposed, especially for the initialization stage. More specifically, the proposed methods rely not only on the enforcement of known distances between markers, but also on the orthogonality of two or three rigidly linked wands. Besides, the proposed ideas utilize common present calibration tools and shorten the typical calibration procedure. The obtained reconstruction accuracy i