Abstract: Highly detailed polygonal surface data can prove difficult to handle and display in a real-time visualization/simulation environment. Level-of-detail techniques are still necessary with today's graphics workstations. An implementation of a quadtree-like recursive subdivision algorithm that divides a rectangular area into sixteen (four by four) areas is described. Continuity of a resulting polygonal mesh is ensured by a traversal step that explicitly joins the edges of regions of different resolution. Similar continuity is also ensured for color and normal vectors associated with each elevation grid point. The result is an unbroken surface with no appreciable discontinuities in color or shading, but increased detail in certain areas selectable by the user (such as target areas, mountains, or areas with less elevation change). This method is specialized for rectangular grid elevation data, but is fast enough to be performed dynamically based on distance of the observer from the terrain. The use of a hextree allows greater decimation for a given number of resolution levels compared to a quadtree, and minimizes the overhead associated with changing resolution levels during traversal for display. Examples shown include a virtual reality fly-over of terrain with a small proportion of mountains (at original full resolution) but a polygon count reduction of 98% overall, yielding more than an order of magnitude frame rate increase. !5
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