Visibility Design Details

• Use a raster terrain elevation database. Why?
  • Simpler
  • Approximate, but...
  • Exact visibility computation on a TIN is so slow, so approximation is needed here also.
• An observer: O.
• Radius of interest: R.
• Observer height above the terrain.
• Target height. Assumed to be a fixed distance above each point of the terrain.
• Viewshed: specific terrain within R of O that is visible from O.
• Visibility Index of O is the fraction of the disk of radius R centered on O that is visible from O.
  • Often computed for every point.
  • Perhaps we want just the most visible points.
  • Identifying them may be more important than calculating their exact visibility indices.
  • Statistical estimation: Choose T random targets within R of R, and counting the number visible.
• Visibility Map: an image representing the visibility index of each original point by a color.