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 ap- plications require efficient algorithms to manipulate the data externally. One of these applications is the viewshed computation that consists in obtain the visi- ble 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 algo- rithm complexity is O(scan(N)) where N is the number of points in a DEM andscan(N) is the minimum number of I/O operations required to readN con- tiguous items stored in the external memory. Also, as shown in the results, our algorithm outperforms the known algorithms described in the literature.

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