[GRASS-user] generating a binary raster map

[gary]

Thanks to the efforts of Bejamin Ducke, I now have r.cva installed. 
However, it does not take a single point as the target, but requires a 
binary raster map containing either targets or viewpoints. I read the 
wiki and did some googling, but can't find out how to build such a map.

If QGIS can do this, I have it installed. I can generate a GPX file if 
that helps.