After the introduction of VRML, 3D Web browsing has become a popular form of networked virtual reality. However, it is still a great challenge for a novice user equipped with a regular desktop PC to navigate in most virtual worlds of moderate complexity. We think the main problem is due to the fact that a user usually uses a 2D mouse to provide low-level navigation control but the display frame rate is not high enough for this servo loop. We consider an alternative metaphor of allowing a user to specify locations of interests on a 2D-layout map and let the system automatically generate the animation of guided tours in virtual architectural environments. Specifically, we aim to generate animations of customizable tour paths and its associated human/camera motions in an on-line manner according to high-level user inputs. We describe an auto-navigation system, in which several efficient path-planning algorithms adapted from robotics are used. This system has been implemented in Java and adopts common VRML browsers as its 3D interface. We also use the geometric model of our departmental building as an example to demonstrate the efficiency and effectiveness of the system.

We consider the problem of automatically generating viewpoint motions for a virtual camera tracking a moving target. Given the target's trajectory, we plan the motion of a camera to maintain visibility with the target while optimizing certain camera-specific criteria, such as preferred view angle or view distance. Previous work has shown that optimal paths for this problem can be found with a dynamic programming approach. However efficiency for this type of approach, even with a simplified view model, is not good enough for interactive applications. We propose an approach that searches for a collision-free path satisfying visibility constraints in the relative configuration space between the moving target and the tracking camera The search is conducted in a best-first fashion according to time and other optimization criteria. We have implemented this algorithm in a software package that is capable of generating such a tracking motion in fractions of a second. This software module is part of a virtual presence system that generates customizable guided tours to assist users in navigating a virtual scene.