Francois Blais

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.

Real-time numerical peak detector

Abstract A very simple and effective peak detector is proposed. The system gives in real-time the position and amplitude of a peak in a digital signal to a precision better than one pixel. An FIR filter is first used to average and differentiate the signal and a linear interpolator to increase the precision of the peak position. A simulated comparison with other techniques is also given. Finally, experimental results with the use of CCD devices are presented.

Review of 20 years of range sensor development

This paper quickly reviews 20 years of development in the field of 3D laser imaging. An overview of 3D digitizing techniques is presented with an emphasis on some of the numerous commercial techniques and systems currently available. This paper covers some of the most important methods that have been developed during the years, both at NRC and elsewhere, with a focus on commercial systems that are good representation of the key technologies that survived the test of the years.

GoLD: interactive display of huge colored and textured models

This paper presents a new technique for fast, view-dependent, real-time visualization of large multiresolution geometric models with color or texture information. This method uses geomorphing to smoothly interpolate between geometric patches composing a hierarchical level-of-detail structure, and to maintain seamless continuity between neighboring patches of the model. It combines the advantages of view-dependent rendering with numerous additional features: the high performance rendering associated with static preoptimized geometry, the capability to display at both low and high resolution with minimal artefacts, and a low CPU usage since all the geomorphing is done on the GPU. Furthermore, the hierarchical subdivision of the model into a tree structure can be accomplished according to any spatial or topological criteria. This property is particularly useful in dealing with models with high resolution textures derived from digital photographs. Results are presented for both highly tesselated models (372 million triangles), and for models which also contain large quantities of texture (200 million triangles + 20 GB of compressed texture). The method also incorporates asynchronous out-of-core model management. Performances obtained on commodity hardware are in the range of 50 million geomorphed triangles/second for a benchmark model such as Stanfords St. Matthew dataset.

Sensors and algorithms for the construction of digital 3-D colour models of real objects

This paper describes sensors and algorithms developed and used for the creation of coloured 3-D triangular meshes from a set of range images with registered colour measurements. The objective is the creation of a digital model of a real object that is compatible with established computer graphics techniques. Triangular meshes are the fundamental rendering primitive supported by most high performance graphics workstations. The surface colour of objects can be represented by attributing reflectance values to the vertices of the mesh. Such a geometric and reflectance model provides a uniform and general representation for sculptured surfaces with non-uniform colouring.

Real world modelling through high resolution digital 3D imaging of objects and structures

Abstract This paper summarises the results achieved from a number of laser scanning experiments performed in our laboratories and on remote sites. The potential of this technology for imaging applications and as an input to virtualised reality environments is discussed. Parameters to be considered for this type of activity are related to the design of laser scanners with adequate depth of field, image resolution, shape reproduction fidelity, registered colour information, robustness to ambient light interference and scanning strategies. The first case reviewed is an application geared towards improving access to art collections belonging to museums. A number of digital 3D models acquired in Italy in 1997–1998 are presented, e.g. marble statue from G. Pisano (circa 1305). The second case aims at digitising large structures. Examples of a large sculpture located outside of the Canadian Museum of Civilisation in Hull, Canada and the Orbiter Docking System (ODS) located at the Kennedy Space Center in Florida, are presented.

Compact three-dimensional camera for robotic applications

A new geometry for the acquisition of three-dimensional coordinates of points on the surfaces of objects is described. It is based on the use of a pattern projected onto the scene and a mask in the aperture of an objective lens. A compact charge-coupled-device camera is used to make the three-dimensional measurements. Experimental results are presented.

Comparative evaluation of the performance of passive and active 3D vision systems

Automated digital photogrammetric systems are considered to be passive three-dimensional vision systems since they obtain object coordinates from only the information contained in intensity images. Active 3-D vision systems, such as laser scanners and structured light systems obtain the object coordinates from external information such as scanning angle, time of flight, or shape of projected patterns. Passive systems provide high accuracy on well defined features, such as targets and edges however, unmarked surfaces are hard to measure. These systems may also be difficult to automate in unstructured environments since they are highly affected by the ambient light. Active systems provide their own illumination and the features to be measured so they can easily measure surfaces in most environments. However, they have difficulties with varying surface finish or sharp discontinuities such as edges. Therefore each type of sensor is more suited for a specific type of objects and features, and they are often complementary. This paper compares the measurement accuracy, on various type of features, of some technologically-different 3-D vision systems: photogrammetry-based (passive) systems, a laser scanning system (active), and a range sensor using a mask with two apertures and structured light (active).

Practical Considerations For A Design Of A High Precision 3-D Laser Scanner System

The Laboratory for Intelligent Systems of the Division of Electrical Engineering of the National Research Council of Canada is intensively involved in the development of laser-based three-dimensional vision systems and their applications. Two basic systems have been invented. One, based on a double aperture mask in front of a CCD camera, has been developed for robotic applications and control. The other technique is based on an auto-synchronized scanning principle to provide accurate, fast, and reliable 3-D coordinates. Using the latter method, several prototypes have been developed for the acquisition of 3-D data of objects and for inspection. This paper will describe some practical considerations for the design and implementation of triangulation-based 3-D range sensors with emphasis on the latter triangulation technique. Some applications and results will be presented.