An Efficient Algorithm to Compute the Viewshed on DEM Terrains Stored in the External Memory

Nowadays, there is a huge volume of data about terrains available and generally, these data do not fit in the internal memory. So, many GIS applications require efficient algorithms to manipulate the data externally. One of these applications is the viewshed computation that consists in obtain the visible points from a given point p. In this paper, we present an efficient algorithm to compute the viewshed on terrains stored in the external memory. The algorithm complexity is O(scan(N)) where N is the number of points in a DEM and scan(N) is the minimum number of I/O operations required to read N contiguous items stored in the external memory. Also, as shown in the results, our algorithm outperforms the known algorithms described in the literature.