Thanks. If r.viewshed is fast enough, a Python script could be built that uses r.viewshed to replicate many of the aspects of r.cva.
Michael ____________________ C. Michael Barton Director, Center for Social Dynamics & Complexity Professor of Anthropology, School of Human Evolution & Social Change Arizona State University voice: 480-965-6262 (SHESC), 480-727-9746 (CSDC) fax: 480-965-7671 (SHESC), 480-727-0709 (CSDC) www: http://www.public.asu.edu/~cmbarton, http://csdc.asu.edu On Dec 1, 2011, at 10:44 PM, Hamish wrote: > Michael wrote: >> How does r.viewshed differ from r.los? > > basically it is faster and it scales to large regions well. > > I don't know the exact O()ness level of it, but r.los becomes very quickly > slower after the region size gets bigger than a smallish amount of rows x > columns, to the point where it becomes unusable. > > r.viewshed should be (*testing welcome) an option-for-option drop in > replacement for r.los written by Laura & co. in C++, from the same > family of code as r.terraflow. It has a detailed help page explaining > its algorithm. > > from the code header comments: > * The viewshed algorithm is efficient both in > * terms of CPU operations and I/O operations. It has worst-case > * complexity O(n lg n) in the RAM model and O(sort(n)) in the > * I/O-model. For the algorithm and all the other details see the > * paper: "Computing Visibility on * Terrains in External Memory" by > * Herman Haverkort, Laura Toma and Yi Zhuang. > > additionally as a ray-tracing sort of problem it is ideally suited for > GPU acceleration using OpenCL support(?), along the same lines as Seth's > to-be committed r.sun + OpenCL. So it has a bright future. > > > also in this group of modules, but slightly different, there is/was the > r.cva module for cumulative viewshed analysis. Unfortunately (AFAIU) the > author could never convince the university he worked for to allow him > to release the code for that as GPL. > > > Hamish _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev