[GRASS-web] r.sun

Vaclav Petras wenzeslaus at gmail.com
Wed Nov 20 07:44:00 PST 2013

On Tue, Nov 19, 2013 at 9:00 PM, richard <dungle1227 at gmail.com> wrote:

> i need help with r.sun working on GRASS.. i download the latest  GRASS GIS
> version.. I don’t understand how can r.sun work in grass. please help me
> step by step

Hi, this does not answer your question but you can check r.sun.daily and
r.sun.hourly modules which are available in addons. You can install them
(recommended) or download them and run as script if the installation does
not work. Depending on what you need to do these modules can just do what
you need.

Their documentation is here:


You can see the source code (with r.sun usage) here if it helpful for you:


These modules basically uses r.sun in two ways. r.sun.daily computes
(cumulative) values for one day using something like this:

r.sun elev=elevation asp_in=aspect slope_in=slope day=150 step=0.5
beam_rad=beam_map diff_rad=diff_map refl_rad=refl_map glob_rad=glob_map

(this should be one line)

And r.sun.hourly computes states at one hour using similar command but
without `step` parameter and with `time` parameter, e.g. time=15.5 for 3:30


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