There are two main methods for collecting viewsheds. A grid can be generated, with values either as a Boolean grid of visible/invisible, or whose pixel values denote the number of visible points. The grid-based approach is particularly useful for understanding the visibility characteristics of the whole landscape (see Llobera 2003). The alternative approach is to generate polygons of the visible areas. The advantage of this latter approach is that one set of polygons can be generated for each point, and then clipped to a buffer according to the viewing distance required, rather than re-running the visibility algorithm. Simple overlays using these same polygons can determine whether sites are intervisible, and assess the similarity of viewsheds from different sites.
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Last updated: Thur Nov 11 2004