I need to do a viewshed analysis using GRASS. I've got the DEMs loaded; and I simply want to input several (2-4) points (like 41.12345N, 122.34567W from GPS). What is the simplest, most straightforward, way of accomplishing this?
Please check the manual page of v.in.ascii to import points or GPS import (just see all import options in Menu -> File -> Import.
However, for r.viewshed you give the coordinate pair simply as parameter.
If you want to calculate several viewsheds, run it in a loop via a script.