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

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Sun Jun 15 16:30:31 EDT 2008

Dear GRASS-users,
Dear Mr. Huld,

Please accept my apologies for this long post and for double-posting
this. My "felis" account in the university does not seem to deliver this
messages in the "jrc.it" mail-server.

I have following question about r.sun2 (and r.horizon):

My colleague Dimitris pointed-out that the global_radiation maps
produced with r.sun2 show a higher radiation (for the same elevation
more or less) in north expositions comparing with southern expositions.
I confirm this behaviour after careful examination of the maps I
produced (if interested I could send you a screen-shot or more with
fragment(s) from
our average global_rad map in kJ).

We expect the exact opposite effect on the globa_rad maps. What could be
my mistake?


Details about the map production using the following data:


*slope & aspect produced with r.slope.aspect

*linke turbidity = 5.2
(average value for the region

N: 39:05:38.098741N    S: 38:23:35.098741N   Res: 0:00:03
E: 22:26:13.344612E    W: 21:21:01.344612E   Res: 0:00:03

and for the period April to October = julian days 92 to 304)

*albedo = 0.23

I produced global_radiation maps using r.sun2 based on the following


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

*** Question about r.horizon

The above command gives horizon maps like hortest.45_0, hortest.45_1,
etc. Following the r.sun2 expects something like hortest.45_000,
hortest.45_001, etc.

If r.sun2 expects a specific prefix-pattern for r.horizon maps, why does
r.horizon name its ouput maps different than what r.sun2 expects?


(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


for i in global_rad_*; do r.mapcalc global_daily_avg=global_daily_avg +
$i; echo "...adding map $i"; done


r.mapcalc global_daily_avg=global_daily_avg/212


r.mapcalc global_daily_avg_kJ="int(global_daily_avg * 3.6)"

Kind regards


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