To render a terrain or a self-shadowing texture map whose topography is represented by many sample points, we must determine what part of the sky is visible from each sample point. The direct primary illumination of each point can then be computed for any distribution of sky illumination. This paper presents an efficient and practical method to compute the horizon, or skyline, at all sample points of a terrain.
From the horizons, the radiosity of each point can be determined in two ways: either quickly, using an approximate lighting model that relies upon only the direct primary illuminations, or more accurately, with a progressive radiosity algorithm that uses the direct primary illuminations as the initial point irradiances, for a considerable savings in time.
The new horizon computation method is compared with other methods by Max and by Cabral, Max, and Springmeyer. Experimental results are reported which show that the new method yields more accurate rendered images and takes much less time to process large terrains.
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@techreport{Stewart-tr96,
author = "A. James Stewart",
title = "Fast horizon computation for accurate terrain rendering",
institution = "University of Toronto",
year = "1996",
month = "June",
type = "technical report",
number = "349"
}