Luc Cournoyer

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.

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.

Eye-safe digital 3-D sensing for space applications

This paper focuses on the characteristics and performance of an eye-safe laser range scanner (LARS) with short- and medium-range 3-D sensing capabilities for space applications. This versatile LARS is a precision measurement tool that will complement the current Canadian Space Vision System. The major advantages of the LARS over conventional video-based imaging are its ability to operate with sunlight shining directly into the scanner and its immunity to spurious reflections and shadows, which occur frequently in space. Because the LARS is equipped with two high-speed galvanometers to steer the laser beam, any spatial location within the field of view of the camera can be addressed. This versatility enables the LARS to operate in two basic scan pattern modes: (1) variable-scan-resolution mode and (2) raster-scan mode. In the variable-resolution mode, the LARS can search and track targets and geometrical features on objects located within a field of view of 30 by 30 deg and with corresponding range from about 0.5 to 2000 m. The tracking mode can reach a refresh rate of up to 130 Hz. The raster mode is used primarily for the measurement of registered range and intensity information on large stationary objects. It allows, among other things, target-based measurements, feature-based measurements, and surface-reflectance monitoring. The digitizing and modeling of human subjects, cargo payloads, and environments are also possible with the LARS. Examples illustrating its capabilities are presented.

Digital 3D imaging system for rapid response on remote sites

A compact digital 3D imaging system based on laser triangulation was designed for applications requiring a rapid response on remote sites. Heritage, forensic and industrial applications are among the best fields to benefit from this new technology. This paper focuses on such aspects as the acquisition, calibration, verification, and model creation. These aspects were all optimized to create a versatile system that is compact, i.e. hand portable to a remote site. Emphasis is placed on accuracy verification and monitoring which are critical factors for obtaining high-quality reconstruction of 3D models from multiple range images. A summary of the experimental results acquired in 1997 and 1998 at a number of sites in Italy is presented in this paper.

Portable digital 3-D imaging system for remote sites

A portable digital 3D imaging system based on laser triangulation was designed for the accurate documentation of environments and objects located in remote sites. Cultural heritage and industrial applications are among the best candidates to benefit from this new technology. This paper focuses on such aspects as the acquisition, display, calibration/verification, and especially on model building. These aspects were all optimized to create a versatile system that is truly portable, i.e. hand portable to a remote site. Emphasis is placed on accuracy verification and monitoring which are critical factors for obtaining high-quality reconstruction of 3D models from multiple range images. A summary of the experimental results acquired at a number of sites in Italy is presented in this paper.

Registered intensity and range imaging at 10 mega-samples per second

A video rate laser range finder based on the autosynchronized scanning approach is presented. This range camera simultaneously provides range and intensity information of a scene in EIA-RS-170 format. A spatial resolution of 420 horizontal lines each having 512 pixels was achieved at a rate of 30 images per second. A wide dynamic range in intensity (16 bits) coupled with drift compensation allows this sensor to achieve a range resolution of 8 bits. The volume of view is 50 x 50 x 50 mm3.

Traceable 3D imaging metrology

This paper summarizes the causes of uncertainty in 3D data measurement, some basic theory of 3D imaging that explains the origin of some of these causes, and, describes the properties and performances of a 100 square meter facility to perform research in traceable 3D imaging metrology. Built in 2006, the laboratory space allows accurate measurements of 3D data from devices operating at standoff distances from a few centimeters up to 10 meters. A laminar flow of 20°C air at 50% humidity level is maintained within ±0.1°C. The total volume of air in the lab is changed twice a minute (18000 cfm). This characteristic combined with the air filtering design allows air cleanliness to be exceptionally good (Class 100).

Practical range camera calibration

This paper presents a calibration procedure adapted to a range camera intended for space applications. The range camera, which is based upon an auto-synchronized triangulation scheme, can measure objects from about 0.5 m to 100 m. The field of view is 30 degree(s) X 30 degree(s). Objects situated at distances beyond 10 m can be measured with the help of cooperative targets. Such a large volume of measurement presents significant challenges to a precise calibration. A two-step methodology is proposed. In the first step, the close-range volume (from 0.5 m to 1.5 m) is calibrated using an array of targets positioned at known locations in the field of view of the range camera. A large number of targets are evenly spaced in that field of view because this is the region of highest precision. In the second step, several targets are positioned at distances greater than 1.5 m with the help of an accurate theodolite and electronic distance measuring device. This second step will not be discussed fully here. The internal and external parameters of a model of the range camera are extracted with an iterative nonlinear simultaneous least-squares adjustment method. Experimental results obtained for a close-range calibration suggest a precision along the x, y and z axes of 200 micrometers , 200 micrometers , and 250 micrometers , respectively, and a bias of less than 100 micrometers in all directions.

Eye-safe laser scanner for range imaging

A fast, range imaging, eye-safe laser scanner which uses a synchronized scanning geometry is described. The device operates at a 1.5-microm wavelength and incorporates an Er doped fiber laser as well as an InGaAs position sensitive detector. Factors influencing device performances are presented along with range images obtained at 1.5 microm.

Real-time geometrical tracking and pose estimation using laser triangulation and photogrammetry

Geometrical tracking and pose estimation using the homogeneous UVW inverse spherical coordinate system, directly from range data obtained from a triangulation based range sensor, are demonstrated. The method is shown to be more accurate, reliable, and computationally faster than using the more conventional XYZ Cartesian coordinate system. This is presented through a practical application, by comparing the accuracy and resolution of a 3D laser scanner prototype that geometrically tracks and computes the relative pose of objects in 3D space. The system uses real-time geometrical surface fitting and intensity processing for the detection and tracking of planar targets on an object. A dual-axis laser scanner is used for this demonstration that combines optical triangulation, Lissajous scanning patterns, geometrical tracking, and photogrammetry (spatial resection), to calculate the relative pose of objects in the 3D space.