[GRASS-dev] r.sun and pj_do_proj() calls

[Seth Price]

I'm working on translating r.sun to OpenCL to run on the GPU, but I've  
hit a bit of a snag. I'm hoping y'all can help or at least tell me  
what I'm looking at.

The root of it is that I can't call pj_do_proj() from within the  
OpenCL kernel, so I need to pass that in from the outside. For  
example, on line 1824 of main.c in the current SVN has us calculating  
the lat/long if we aren't passed in files latin and longin. So for the  
OpenCL version I'll need to make latin and longin arrays ahead of time  
instead of calculating it in the loop.

The problem is in rsunlib.c at line 250. How can I avoid this  
pj_do_proj() call? I was thinking that because I have the lat/long  
coordinates for all points, I can use that on lines 255 & 256,  
effectively changing G_projection() to return PROJECTION_LL and  
avoiding going into the 'if' statement. I don't know if that will  
work, though. I really don't know what's going on here enough to feel  
comfortable changing the calculation.

Suggestions? Code?
~Seth