Abstract. We present a new active vision technique called zoom tracking. Zoom tracking is the continuous adjustment of a camera's focal length in order to keep a constant-sized image of an object moving along the camera's optical axis. Two methods for performing zoom tracking are presented: a closed-loop visual feedback algorithm based on optical flow, and use of depth information obtained from an autofocus camera's range sensor. We explore two uses of zoom tracking: recovery of depth information and improving the performance of scale-variant algorithms. We show that the image stability provided by zoom tracking improves the performance of algorithms that are scale variant, such as correlation-based trackers. While zoom tracking cannot totally compensate for an object's motion, due to the effect of perspective distortion, an analysis of this distortion provides a quantitative estimate of the performance of zoom tracking. Zoom tracking can be used to reconstruct a depth map of the tracked object. We show that under normal circumstances this reconstruction is much more accurate than depth from zooming, and works over a greater range than depth from axial motion while providing, in the worst case, only slightly less accurate results. Finally, we show how zoom tracking can also be used in time-to-contact calculations.

Large, complex 3D scenes are best rendered in an output-sensitive way, i.e., in time largely independent of the entire scene model's complexity. Occlusion culling is one of the key techniques for output-sensitive rendering. We generalize existing occlusion culling algorithms, intended for static scenes, to handle dynamic scenes having numerous moving objects. The data structure used by an occlusion culling method is updated to reflect the objects' possible positions. To avoid updating the structure for every dynamic object at each frame, a temporal bounding volume (TBV) is created for each occluded dynamic object, using some known constraints on the object's motion. The TBV is inserted into the structure instead of the object. Subsequently, the object is ignored as long as the TBV is occluded and guaranteed to contain the object. The generalized algorithms' rendering time is linearly affected only by the scene's visible parts, not by hidden parts or by occluded dynamic objects. Our techniques also save communications in distributed graphic systems, e.g., multiuser virtual environments, by eliminating update messages for hidden dynamic objects. We demonstrate the adaptation of two occlusion culling algorithms to dynamic scenes: hierarchical Z-buffering and BSP tree projection.

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Abstract

A single adaptable user interface (ACll) which allows the user to switch between any number of different dialogue modes at any time-even in the middle of a command-can be useful to a variety of users who are neither beginners nor experts. It can also be used in applications where different dialogue modes are appropriate for the various parameters of a singie command. An implemented user interface management system (CIIMS) suggests the practicality of ACJIs and their automatic generation.