[GRASS-user] [GRASSLIST:1178] how to use cloud cover with r.sun?

[Hamish]

> But is it really possible that the r.sun module (i'm using Grass 6.0.1
> on Ubuntu Breezy) would treat elevation in degrees??

Yes, it is possible. Maybe even likely.


> And can you please tell me where the 1852*60 comes from?

There are 1852 meters in a nautical mile. There are 60 nautical miles in
a degree of latitude.  elev_in_meters / (1850.0 * 60) = elevation in deg

The width of a deg longitude is equal to width_lat*cos(lat).

If rescaling the elevation into degress be sure to /(1852.0*60). This
ensures that the result will be a floating point value (as opposed to
 /(1852*60) ).


> I guess i would have to creat a new location in UTM coordinates and
> then do the projecting back and forth you suggest..

I think this is the saner solution, but I expect that a single UTM zone
is not an appropriate projection for working with an area the size of
India.

Markus wrote:
> This should be a projection covering the entire subcontinent
> in a reasonable way - what are the official projection(s) for
> that area?

If you have problems finding one, you might ask for help on the PROJ.4
mailing list.



Hamish