ISPRS Congress, Vienna, 1996, Intl. Archives of Photogrammetry, Commission V, pp 140-146.
TWO 3-D SENSORS FOR ENVIRONMENT MODELING AND VIRTUAL REALITY: CALIBRATION AND MULTI-VIEW REGISTRATION
S.F. El-Hakim, J.-A.Beraldin, G. Godin, and P. Boulanger
Institute for Information Technology, National Research Council
Ottawa, Ontario, Canada
Commission V, Working Group 1
KEY WORDS: Calibration, Modeling, Registration, Graphics, Scanner, Real-time, Three-dimensional, Virtual-Reality.
Virtual environments (VEs) also known as virtual reality (VR) are increasingly being considered for industrial, medical, and educational / training applications, to name a few. A VE provides real-time interaction with 3-D models when combined with a display technology that gives the user immersion in the model world and direct manipulation of objects. In many of the applications, the truthful representation of the environment and the accurate manipulation and navigation in the virtual world are crucial. In this paper we examine the potential use of laser range cameras and digital photogrammetry in the accurate creation of VE models of real scenes and in the tracking of the user for precise interaction with models.
Virtual environments are defined as the real-time graphics interaction with three-dimensional models, when combined with a display technology that gives the user immersion in the model world and direct manipulation (Bishop and Fuchs, 1992.) The technology will radically change the way people interact with computers and allow them to act as if they were in places they are not. Obviously, the entertainment industry is the leading market, however many other applications do exist. For example, training such as flight simulators, industrial design and prototyping (Hedberg, 1996), medical (Goble, et al, 1995), and military (Polis et al, 1995) applications are now employing the technology. VE is currently advancing at a very rapid pace in both research organizations and industry. There are many useful publications that may serve as introduction to the topic and document the state of the technology (e.g. Adams, 1993, Azuma, 1995, Bishop and Fuchs, 1992, Phillips-Mahoney, 1995, Sturman and Zelter, 1994, and Stevens, 1994). We will only give a brief overview here.
1.1. Overview of VE Technology
Virtual exploring of real places and environments, either for leisure, engineering design, simulations, or tasks in remote hazardous environments, is more effective and useful if geometrical relationships and dimensions in the virtual model are accurate. Also, since in VE the rendering of images must respond immediately to one's movements, the relationship between the viewer's head and hands and the 3-D environment must be continuously and accurately known. This is also true for interacting with and manipulating objects in that environment. The degree of accuracy of the modeling and positioning will widely vary with applications. Even within an application the accuracy requirements may vary. For example, the accuracy of the spatial location and orientation of doors and openings through which the viewer or moving platforms will go, is higher than other details.
Figure 1 summarizes the main components of a VE system. First, the 3-D world has to be created. The "computer-generated" environment can be a truthful representation of the "real" environment if precise, well-calibrated, laser range cameras are used to digitize the latter to create the former.
However, for several reasons such as availability and cost, most models are built by either using standard geometric primitives, libraries of pre-modeled objects, or manual digitizing of every point. Building such a model graphically for a detailed environment takes enormous efforts and time and may look unrealistic. On the other hand , digitizing the environment with laser range cameras is an excellent alternative to graphically creating the model. It saves time and effort while providing a more realistic model. Real-world 3-D image-based VE can advantageously complement or replace artificially created VE in many endeavors. Currently, creating such models of the real world remains an obstacle for this technology and is a limitation to the implementation in a wide range of useful applications. Other components of the VE system include the head trackers, the image rendering engine, and the 3-D display (either head mounted or one or more computer screen). The rate of all the processes must be fast enough to update the display at 20 Hz or faster.