Back-to-Front Ordering of Triangles in Digital Terrain Models over Regular Grids

摘要

Visiting triangles that conform a digital terrain model is a core operation in a number of fields like animationand video games or generating profiles, cross-sections, and contours in civil engineering. Perfornfing the visit in an efficientmanner is an issue specially when the output of the traversal depends in some way on additional parameters or informationchanging over time, for example, a moving point of view. In this work we report a set of rules that, given a digital terrainmodel defined over a regular grid and an arbitrary point of view outside the terrain, define a total back-to-front order in theset of digital terrain model triangles with respect to the point. The set of rules is minimal, complete and correct. To assesshow the rules perform, we have implemented a CPU-based algorithm for realistically rendering height fields defined overregular grids. The algorithm does not make use of the z-buffer or shaders featured by our graphics card. We show how ouralgorithm is implemented and show visual results obtained from synthetic and real data. We further discuss the algorithmperformance with respect to two algorithms： a naive algorithm that visits triangles according to grid indices and does notsolve the hidden line problem, and the z-buffer provided by the graphics card featured by our computer. Our algorithmallows real-time interaction when the point of view arbitrarily moves in 3D space and we show that its performance is asgood as that of the z-buffer graphics card.