calculates the viewshed around an given observer in the traditional method. It runs a separate LOS from the observer to each point within the circle, and sees whether any elevations on that LOS obstruct it. If the range is R, then the execution time is proportional to R cubed. can handle user-specified regions of interest; they do not need to be circles around the observer.
Proc-LOS was used for massive visibility index calculations on about 20 DTED cells on the Korean peninsula.