From GRASS-Wiki
Revision as of 02:53, 17 August 2009 by HamishBowman (talk | contribs) (Seed maps: colorize)

Jump to: navigation, search

Help page


The speed of r.sun is much higher if r.horizon is used first and the resulting maps are given as input to r.sun. Background: the horizon needs to be computed only one time before, not in every step within r.sun. See the example at the end of the r.sun help page.


Create an artificial surface containing a Gaussian mound:

r.surf.volcano out=gauss method=gaussian kurtosis=1

Overlay some 200m contours to show underlying topography:

r.contour in=gauss out=gauss_200m_contours step=200
d.vect gauss_200m_contours color=white

Set map's color table to highlight detail:

r.colors rad_test.day355.beam col=bcyr -e
d.legend rad_test.day355.beam range=1300,1500

Time step

The following three images demonstrate the effects of using different time step parameters.

r.sun -s elevin="gauss" glob_rad="rad.global.30minT" day=180 step=0.5
Default 30 minute time step over a Gaussian mound.

r.sun -s elevin="gauss" glob_rad="rad.global.15minT" day=180 step=0.25
15 minute time step over a Gaussian mound.

r.sun -s elevin="gauss" glob_rad="rad.global.03minT" day=180 step=0.05
3 minute time step over a Gaussian mound.

The 3 minute time step takes roughly ten times as long to run as the 30 minute timestep.

Seed maps

Using seed maps can greatly speed up processing. This is especially important if you will batch process e.g. for every day of the year.

  • aspin= and slopein= options: create slope and aspect maps with the r.slope.aspect module.
Caution: currently buggy. See trac #498.
Estimated speedup:  ?%.

  • horizon= and horizonstep= options: Pre-calculate horizon shadows by creating a series of horizon rasters with the r.horizon module.
Results not as smooth as without using this option?? See trac #498.
Estimated speedup:  ?%.

  • latin= option: Pre-calculate latitudes for each raster cell.

The following script will create a raster containing latitude as the raster value:

 # create latitude map (WGS84)
 g.region rast=elevation.dem
 r.mapcalc one=1
 r.out.xyz one | \
   cut -f1,2 -d'|' | \
   m.proj -oed --quiet | \
   sed -e 's/[ \t]/|/g' | \
   cut -f1,2,4 -d'|' | \
   r.in.xyz in=- out=elevation.lat
 g.remove one
Estimated speedup:  ?%.
See trac #498.


  • Add support for OpenMP parallelization