Efficient viewshed computation on terrain in external memory

The recent availability of detailed geographic data permits terrain applications to process large areas at high resolution. However the required massive data processing presents significant challenges, demanding algorithms optimized for both data movement and computation. One such application is viewshed computation, that is, to determine all the points visible from a given point p. In this paper, we present an efficient algorithm to compute viewsheds on terrain stored in external memory. In the usual case where the observer's radius of interest is smaller than the terrain size, the algorithm complexity is theta(scan(n (2))) where n (2) is the number of points in an n x n DEM and scan(n (2)) is the minimum number of I/O operations required to read n (2) contiguous items from external memory. This is much faster than existing published algorithms.