[GRASS-user] Usage of R.Sun

Daniel Lee lee at isi-solutions.org
Thu Dec 27 04:20:11 PST 2012

Hi Paul,

Please don't send me questions directly - as much as I like to help you
out, I think that the list is a lot more reliable and when I can I answer
there as well. I've CC'd this to the user list, in case other people have
some ideas too. Answers are inline.

2012/12/27 Paul Meems <bontepaarden at gmail.com>

> Hi Daniel,
> I've finally got some time to look into GRASS.
> I've downloaded GRASS GIS 6.4.3RC2.
> I've found the sun radiation plug-in (r.sun). A lot of settings can be set
> ;) I'll look into it and perhaps ask you some questions later.
> My first question is how to load my data?
> My 0.5m DEM is a directory of 39 folders with ARCGIS Binary Grids
> (sta.adf). Should I first merge them into 1 large GeoTiff?
> The size of my area is about 32 km2.
> I've tried opening the adf files in Grass, but I'm not sure how to do
> that. Dropping the file didn't work. Using 'Import raster data' seems to
> work.
> Is that the correct one?

Yes, that's correct. In GRASS, it's best practice to *always* import data
before you work with it. This has a lot of advantages which I won't get
into here, but the main one in my view is that you never have to worry
about the data's format again.

If you want, merge the rasters using some other tool into a GeoTIFF. If I'm
not mistaken, GeoTIFF has a restriction on file size, meaning that rasters
cannot be larger than 4 GB. Depending on the resolution of your rasters,
this could be a problem. GRASS has no problem importing GeoTIFFs, and the
size of the rasters is determined by the number of cells and their value
ranges, not by the size of the area itself.

Here's a good set of instructions on importing *.adf files into GRASS:

> As mentioned by you before Grass calculates the solar radiation on a daily
> bases. I assume I can create a batch file to calculate the solar radiation
> for the whole year, but then I end up with 365 new files. I assume I need
> to add all values to 1 new raster. Which plug-in should I use for this?

You're looking at a classic raster calculator operation. That can be done
with r.mapcalc. It's got a great manual that covers all of the options you
might be interested in :)

> I hope you can help me. Grass has a steep learning curve and without some
> help it will be hard for me.

Just keep with it, GRASS does have a steep learning curve but it's a very
logical GIS and I've never regretted the time I spent getting to know it.
Just don't be afraid to read the manuals, use Google and ask questions and
you'll be fine :) Looks like you're right on track.

Cheers and happy New Years,
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