地形可视域分析是地形分析的重要组成部分，针对现有方法存在的复杂度高、通用性差等问题，提出一种基于距离场映射的地形可视性分析方法。首先，在观察点位置以透视投影渲染地形，将观察点到可见的地形表面点的距离作为输出，保存到距离图；然后，以顶视图平行投影的方式再次渲染地形，通过对比片元到观察点的距离值与片元的距离场映射值来判断片元的可见性；最后，给出一种偏移采样法来减小锯齿走样的影响。试验表明，这种方法可以快速获得较高精度的可视域计算结果。另外，这种方法几何无关，能适用于多种形式的三维地形模型以及地物的可视性分析。%Terrain viewshed analysis is an important content of terrain analysis, and a new method based on distance field mapping is given to solve the problems the existing methods have, such as complexity in computation and bad applicability. First, the terrain was rendered with perspective projection from the view point, and the distance between the view point and the visible points on terrain surface was saved into a distance map as output; then, the terrain was rendered again with orthogonal projection from top view, and the visibility of the fragment was obtained by comparing the distance from the fragment to the view point and the distance field mapping value. At last, a displaced sampling method was given to reduce the aliasing artifacts, Results show： the method can efficiently yield visibility results of high accuracy~ in addition, it is applicable for different terrain models even with objects on them, because the algorithm is independent of geometry.
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