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A visual navigation system is described which uses texture mapped primitives to represent clusters of objects to maintain high and approximately constant frame rates. In cases where there are more unoccluded primitives inside the viewing frustum than can be drawn in real-time on the workstation, this system ensures that each visible object, or a cluster that includes it, is drawn in each frame. The system supports the use of traditional “level-of-detail” representations for individual objects, and supports the automatic generation of a certain type of level-of-detail for objects and clusters of objects. The concept of choosing a representation from among those associated with an object that accounts for the direction from which the object is viewed is also supported. The level-of-detail concept is extended to the whole model and the entire scene is stored as a hierarchy of levels-of-detail that is traversed top-down to find a good representation for a given viewpoint. This system does not assume that visibility information can be extracted from the model and is thus especially suited for outdoor environments.
Maciel et al. (Sun,) studied this question.