[GRASS-user] Question about r.sun2 and r.horizon

[Nikos Alexandris]

On Sun, 2008-06-15 at 22:30 +0200, Nikos Alexandris wrote:
> 1.

> r.horizon elevin=srtm3_stel step=45 horizon=horizon_45 coord=4275945

# This is a bug and will be fixed.

> 2.
> (using r.sun2 in a loop)
> 
> for i in `seq 92 304`; do r.sun2 -s --o  elevin=srtm3_stel
> aspin=aspect_stel slopein=slope_stel alb=0.23 lin=5.2 lat=4275945
> horizon=horizon.45 horizonstep=45 glob_rad=global_rad_$i day=$i; done

I created latitude and longitude maps, re-run r.sun2 and compared a day
(on derived from the above command and another one derived from the
command below). The results seem rational now.

r.sun2  -s  elevin=srtm3_for_global_rad  aspin=aspect_for_global_rad
slopein=slope_for_global_rad  alb=0.23  lin=5.2
latin=latitude_for_global_rad  longin=longitude_for_global_rad
horizon=horizon.45  horizonstep=45  glob_rad=global_rad_testday92 day=92

So the question is now, why when using a fixed lat value, the northern
expositions have a higher radiation than the southern expositions?