[GRASS-user] r.sunmask cast shadow question

[Markus Neteler]

On Sat, Jan 4, 2014 at 12:17 PM, Tim Michelsen
<timmichelsen at gmx-topmail.de> wrote:
...
> Perhaps r.sun.hourly should get
...
> * average sunlight duration per day during a month, etc. (h/d)

This needs some modifications in the r.sun code. I was discussing this
issue some time ago with Jaro Hofierka who gave the following hints:

On Thu, Apr 16, 2009 at 18:34, Jaro Hofierka <hofierka at geomodel.sk> wrote:
> Markus,
>
> sunrise, sunset times are calculated for each cell, however, not including
> shadows by surrounding terrain features. This would need another test which
> in fact is done during radiation calculations (there is a time step to sum
> up radiation), but the time is not stored.
> To minimize a number of output maps we have stored the information of
> sunrise/sunset times using min-max values in a history file (or a single
> value when a single value of latitude is used for the map). So it would need
> a modification of the code to put there extra files storing sunrise-sunset
> times. If you need a quicker solution, you would need to make tests just for
> a small part of the day (e.g. 1-2 hours around reported sunrise/sunset
> times).
>
> Jaro

Perhaps useful as a pointer.

Markus