I have a raster surface model and I'm trying to determine the height an object would need to be at to be visible from an arbitrary point at an arbitrary altitude.
I am currently using Grass and have tried r.viewshed, while it does seem to be able to generate an elevation delta between the raster and the observer, I do not see a way to generate a delta between the raster and the line of sight at every point. my expectation is that everything that is directly visible would have a value of 0, and then shadowed areas would indicate the minimum height an object would be visible at.
While I am using GRASS at the moment, I am not against considering another piece of software.
Anybody have any ideas? or am I going to have to pull the source for viewshed and modify it?