Marc Rioux

Laser ranging : a critical review of usual techniques for distance measurement

We review some usual laser range finding techniques for in- dustrial applications. After outlining the basic principles of triangulation and time of flight (pulsed, phase-shift and frequency modulated continu- ous wave (FMCW)), we discuss their respective fundamental limitations. Selected examples of traditional and new applications are also briefly presented.

Laser range finder based on synchronized scanners.

A new geometrical arrangement is proposed to improve performances of optical triangulation. Two scanners in synchronization allow a linear position sensor to be used for surface topography measurement. Besides a large increase in speed of measurement (approximately megahertz), the new geometry allows considerable reduction of the optical head size compared with usual geometries, so the shadow effects are reduced proportionally. It also provides a means to obtain a very large field of view without compromising on resolution. Geometrical analysis and experimental results are presented.

Description of shape information for 2-D and 3-D objects

The description of the spatial characteristics of two- and three-dimensional objects, in the framework of MPEG-7, is considered. The shape of an object is one of its fundamental properties, and this paper describes an efficient way to represent the coarse shape, scale and composition properties of an object. This representation is invariant to resolution, translation and rotation, and may be used for both two-dimensional (2-D) and three-dimensional (3-D) objects. This coarse shape descriptor will be included in the eXperimentation Model (XM) of MPEG-7. Applications of such a description to search object databases, in particular the CAESAR anthropometric database are discussed.

Three-dimensional surface anthropometry: Applications to the human body

Abstract Anthropometry is the study of the measurement of the human body. By tradition this has been carried out taking the measurements from body surface landmarks, such as circumferences and breadths, using simple instruments like tape measures and calipers. Three-dimensional (3D) surface anthropometry enables us to extend the study to 3D geometry and morphology of mainly external human body tissues. It includes the acquisition, indexing, transmission, archiving, retrieval, interrogation and analysis of body size, shape, and surface together with their variability throughout growth and development to adulthood. While 3D surface anthropometry surveying is relatively new, anthropometric surveying using traditional tools, such as calipers and tape measures, is not. Recorded studies of the human form date back to ancient times. Since at least the 17th century 1 investigators have made attempts to measure the human body for physical properties such as weight, size, and centre of mass. Martin documented ‘standard’ body measurement methods in a handbook in 1928. 2 This paper reviews the past and current literature devoted to the applications of 3D anthropometry because true 3D scanning of the complete human body is fast becoming a reality. We attempt to take readers through different forms of technology which deal with simple forms of projected light to the more complex advanced forms of laser and video technology giving low and/or high resolution 3D data. Information is also given about image capture of size and shape of the whole as well as most component parts of the human body. In particular, the review describes with explanations a multitude of applications, for example, medical, product design, human engineering, anthropometry and ergonomics etc.

Influence of speckle on laser range finders

Speckle noise is shown to constitute a fundamental limit to laser range finders based on triangulation. A model is derived that relates the magnitude of this noise to the optical geometry used. Synchronized laser scanners are shown to have inherent speckle noise reduction properties. Experimental results are presented.

Color reflectance modeling using a polychromatic laser range sensor

A system for simultaneously measuring the 3-D shape and color properties of objects is described. Range data are obtained by triangulation over large volumes of the scene, whereas color components are separated by means of a white laser. Details are given concerning the modeling and the calibration of the system for bidirectional reflectance-distribution functions measurements. A reflection model is used to interpret the data collected with the system in terms of the underlying physical properties of the target. These properties are the diffuse reflectance of the body material, the Fresnel reflectance of the air media interface, and the slope surface roughness of the interface. Experimental results are presented for the extraction of these parameters. By allowing the subtraction of highlights from color images and the compensation for surface orientation, spectral reflectance modeling can help to understand 3-D scenes. A practical example is given where a color and range image is processed to yield uniform regions according to material pigmentation. >

Recognition and shape synthesis of 3-D objects based on attributed hypergraphs

A computer vision system is presented for shape synthesis and recognition of three-dimensional objects using an attributed hypergraph representation. The vision system is capable of: (1) constructing an attributed hypergraph representation (AHR) based on the information extracted from an image with range data; (2) synthesizing several AHRs obtained from various views of an object to form a complete AHR of the object; and (3) recognizing any view of an object of finding the graph monomorphism between the AHR of that view and the complete AHR of a prototype object. This system is implemented on a Grinnell imaging system driven by a VAX 11/750 running VMS. >

A texture-mapping approach for the compression of colored 3D triangulations

We present an algorithm that constructs compact and realistic descriptions of colored 3D objects using texture mapping on compressed triangulations. A high-resolution triangular mesh model is created by integrating measurements from a color 3D laser sensor. Each vertex is attributed with a RGB color value. The high-resolution triangulation is transformed into a compressed triangulation and a texture map. This map embeds the color information of the vertices removed during the geometric compression and projected on the lower resolution triangulation. We describe the algorithm for the rapid and efficient construction of a texture map for compressed triangulations of arbitrary topology. Experiments show that high compression rates can be achieved while maintaining good visual similarity between the original and compressed models.

Object model creation from multiple range images: acquisition, calibration, model building and verification

This paper demonstrates the accuracy of a prototype Laser Range Camera (LRC) developed at the National Research Council of Canada for the creation of models of real objects. A laser survey performed in collaboration with the Canadian Space Agency and NASA is used as a test case. The object selected for this particular test case is the Orbiter Docking System (ODS) located at the Kennedy Space Center, Florida. During the laser survey, 128 range (and registered intensity) images were acquired all around the ODS. These images were then processed in our laboratory. A full model of the top portion of the ODS was created along with an almost complete model of the ODS. The ODS has a diameter of 1.6 m and a height of 3.9 m. Targets mounted on the top portion of the ODS were used to assess the accuracy of the calibration and of the image registration process. These targets were measured with a network of theodolites a day prior to the laser survey and used as a reference. With the current calibration and range image registration techniques, an accuracy better than 0.25 mm in X and Y, and, 0.80 mm in Z was achieved. These results compare favorably with the single point accuracy obtained after calibration, i.e., about 0.25 mm in X and Y, and, 0.50 mm in Z. These figures and others should testify on the usefulness of a LRC for accurate model building.

Active optical 3D imaging for heritage applications

High-resolution 3D imaging and modeling is an important application in the heritage field. We describe several demonstration projects conducted in collaboration with museums and conservation agencies.