Higher isn't Necessarily Better: Visibility Algorithms and
			   Experiments

		       Wm Randolph Franklin
		 Rensselaer Polytechnic Institute
		       Troy, NY, 12180 USA

			 LTC Clark K Ray
    Department of Electrical Engineering and Computer Science
		      U.S. Military Academy
		     West Point, NY 10996 USA

			   May 28, 1994

     Symposium on Spatial Data Handling, Edinburgh, Sept 1994


      We describe several fast programs to compute viewsheds and
      weighted visibility indices for observation points in a raster
      terrain.  These programs explore various tradeoffs between speed
      and accuracy.  We have analyzed many cells of data; there is no
      strong correlation between a point's elevation and its weighted
      visibility index.  However, the, very few, high visibility points
      tend to characterize features of the terrain.  This work can form
      a basis for automatically locating observers jointly to cover a
      terrain region of interest.