[GRASS5] Angle of incidence in viewshed/line of sight

[Hamish]

> Just so we don't re-invent the wheel, has anyone developed the code
> for evaluating the angle of incidence from a single point in the
> landscape (i.e. the point used for r.los) to cells within the
> viewshed? I am analyzing repeated historical topographic survey
> photographs (more on this later) and want to account for components of
> registration and classification error due to terrain (angle of
> incidence). I have looked at the code for r.los and r.sun and will be
> seeking help from some students in our new computer science/geomatics
> programme as I am not (yet) a programmer. Look forward to any
> suggestions...


Yes, I have done this some time ago.

I modified r.los to return horizontal angle to target instead of
vertical angle to target for the values in the resultant raster map. This
was for GRASS 5.0, but it should work for 6.0 just as well I think. If
you want I can supply the code.

r.los is a real mess and doesn't scale well to larger grid sizes.

Be sure to check out r.cva as well:
  http://www.ucl.ac.uk/~tcrnmar/GIS/r.cva.html


r.sunmask with altitude and azimuth options might be another way.



Hamish