Jean-Angelo Beraldin

Fusion of range camera and photogrammetry: a systematic procedure for improving 3-D models metric accuracy

The generation of three-dimensional (3-D) digital models produced by optical technologies in some cases involves metric errors. This happens when small high-resolution 3-D images are assembled together in order to model a large object. In some applications, as for example 3-D modeling of Cultural Heritage, the problem of metric accuracy is a major issue and no methods are currently available for enhancing it. The authors present a procedure by which the metric reliability of the 3-D model, obtained through iterative alignments of many range maps, can be guaranteed to a known acceptable level. The goal is the integration of the 3-D range camera system with a close range digital photogrammetry technique. The basic idea is to generate a global coordinate system determined by the digital photogrammetric procedure, measuring the spatial coordinates of optical targets placed around the object to be modeled. Such coordinates, set as reference points, allow the proper rigid motion of few key range maps, including a portion of the targets, in the global reference system defined by photogrammetry. The other 3-D images are normally aligned around these locked images with usual iterative algorithms. Experimental results on an anthropomorphic test object, comparing the conventional and the proposed alignment method, are finally reported.

Range imaging sensors development at NRC Laboratories

Laser range finders can be used in a variety of geometries to match requirements of applications such as robot vision, inspection, prosthesis fabrication, CAD/CAM, computer graphics, and automatic assembly. A review is presented of the development of five prototypes which have specified advantages for a class of applications. One of these is based on the use of a mask with a conventional TV camera lens, and the others are variations of synchronized laser scanners. Also described is a segmentation technique based on Fourier transformations and a database of 3D images that are made available for computer vision researchers.<<ETX>>

High-resolution digital 3D imaging of large structures

This talk summarizes the conclusions of a few of these laser scanning experiments on remote sites and the potential of the technology for imaging applications. Parameters to be considered for these types of activities are related to the design of a large volume of view laser scanner, such as the depth of field, the ambient light interference (especially for outdoors) and, the scanning strategies. The first case reviewed is an inspection application performed in a coal- burning power station located in Alberta, Canada. The second case is the digitizing of the ODS (Orbiter Docking System) at the Kennedy Space Center in Florida and, the third case is the digitizing of a large sculpture located outside of the Canadian Museum of Civilisation in Ottawa-Hull, Canada.

Best practices for the 3D documentation of the Grotta dei Cervi of Porto Badisco, Italy

The Grotta dei Cervi is a Neolithic cave where human presence has left many unique pictographs on the walls of many of its chambers. It was closed for conservation reasons soon after its discovery in 1970. It is for these reasons that a 3D documentation was started. Two sets of high resolution and detailed three-dimensional (3D) acquisitions were captured in 2005 and 2009 respectively, along with two-dimensional (2D) images. From this information a textured 3D model was produced for most of the 300-m long central corridor. Carbon dating of the guano used for the pictographs and environmental monitoring (Temperature, Relative humidity, and Radon) completed the project. This paper presents this project, some results obtained up to now, the best practice that has emerged from this work and a description of the processing pipeline that deals with more than 27 billion 3D coordinates.

Short- and medium-range 3D sensing for space applications

This paper focuses on the characteristics and performance of a laser range scanner (LARS) with short and medium range 3D sensing capabilities for space applications. This versatile laser range scanner is a precision measurement tool intended to complement the current Canadian Space Vision System (CSVS). Together, these vision systems are intended to be used during the construction of the International Space Station (ISS). Integration of the LARS to the CSVS will allow 3D surveying of a robotic work-site, identification of known objects from registered range and intensity images, and object detection and tracking relative to the orbiter and ISS. The data supplied by the improved CSVS will be invaluable in Orbiter rendez-vous and in assisting the Orbiter/ISS Remote Manipulator System operators. 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 level of 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 degrees X 30 degrees and with corresponding range from about 0.5 m to 2000 m. This flexibility allows implementations of practical search and track strategies based on the use of Lissajous patterns for multiple targets. The tracking mode can reach a refresh rate of up to 137 Hz. The raster mode is used primarily for the measurement of registered range and intensity information of large stationary objects. It allows among other things: target-based measurements, feature-based measurements, and, image-based measurements like differential inspection in 3D space and surface reflectance monitoring. The digitizing and modeling of human subjects, cargo payloads, and environments are also possible with the LARS. A number of examples illustrating the many capabilities of the LARS are presented in this paper.

GD&T-Based Characterization of Short-Range Non-contact 3D Imaging Systems

We present a series of test metrics, artifacts, and procedures for characterizing and verifying the operating limits of a short-range non-contact three-dimensional imaging system. These metrics have been designed to correspond to dimensioning and tolerancing metrics that are widely used in industry (e.g. automotive, aerospace, etc.). We introduce operating limit metrics that correspond with the geometric dimensioning and tolerancing (GD&T) metrics of Form (Flatness and Circularity), Orientation (Angularity), Location (Sphere, Corner, and Hole Position Errors), and Size (Diameter, Sphere-spacing, Plane-spacing and Angle Errors). An example is presented to illustrate how these metrics, artifacts, and associated test procedures can be used in practice.

Lateral resolution challenges for triangulation-based three-dimensional imaging systems

Lateral resolution is a particularly challenging concept to quantify in triangulation-based three-dimensional (3-D) imaging systems. We present these challenges, then describe an artifact-based methodology for evaluating the lateral resolution of a triangulation-based 3-D imaging system that uses laser spots or laser lines. In particular, the response of a 3-D imaging system to a spatial discontinuity (step edge) has traditionally been modeled as a first-order linear system. We model the response of a triangulation-based laser imaging system to a spatial step edge from first principles and demonstrate that the response should be modeled as a non linear system. This model is then used as a basis for evaluating the lateral (structural) resolution of a triangulation-based laser imaging system.

Hierarchical characterization procedures for dimensional metrology

We present a series of dimensional metrology procedures for evaluating the geometrical performance of a 3D imaging system that have either been designed or modified from existing procedures to ensure, where possible, statistical traceability of each characteristic value from the certified reference surface to the certifying laboratory. Because there are currently no internationally-accepted standards for characterizing 3D imaging systems, these procedures have been designed to avoid using characteristic values provided by the vendors of 3D imaging systems. For this paper, we focus only on characteristics related to geometric surface properties, dividing them into surface form precision and surface fit trueness. These characteristics have been selected to be familiar to operators of 3D imaging systems that use Geometrical Dimensioning and Tolerancing (GD&T). The procedures for generating characteristic values would form the basis of either a volumetric or application-specific analysis of the characteristic profile of a 3D imaging system. We use a hierarchical approach in which each procedure builds on either certified reference values or previously-generated characteristic values. Starting from one of three classes of surface forms, we demonstrate how procedures for quantifying for flatness, roundness, angularity, diameter error, angle error, sphere-spacing error, and unidirectional and bidirectional plane-spacing error are built upon each other. We demonstrate how these procedures can be used as part of a process for characterizing the geometrical performance of a 3D imaging system.

Sensors optimized for 3-D digitization

This paper presents our activities on VLSI optosensors optimized for three-dimensional vision. A description of the integrated devices jointly developed for industrial and scientific applications will be given. All the sensors presented here have been fabricated using standard CMOS technology that allows the monolithic integration of photo-sensors, together with readout circuits, and digital signal processors.

Evaluating Dense 3D Surface Reconstruction Techniques using a Metrological Approach

Abstract: This paper discusses an approach for evaluating the accuracy of dense 3D surface reconstruction techniques based on images. So far, the emergence of these novel techniques has not been supported by the definition of an internationally recognized standard which is fundamental for user confidence and market growth. In order to provide an element of reflection and solution to the different communities involved in image-based 3D modeling, we present an approach for the assessment of the metric performance of an open-source set of routines for bundle block adjustment and dense image matching (Apero/MicMac). The evaluation is performed using a metrological approach, through comparisons between image-based 3D generated data and ‘reference’ data acquired with two hemispherical laser scanners, one total station, and one laser tracker. Aspects of traceability and measurement uncertainty of all these reference 3D data are discussed. The methodology is applied to two case studies, tailored to analyze the software capabilities in dealing with both outdoor and environmentally controlled conditions. Comparative data and accuracy evidence provided by both tests allow the study of some key factors affecting 3D model accuracy.