[GRASS-user] How to aggregate values of a raster to an area specified by a polygon?

[TimNorwey]

Hy all,

I´m calculating solar values using r.sun. As you know the result is a
raster, representing values of global total irradiance.

Beside of this raster I have a shapefile including the footprints of houses.

What I´m planning to do, is to aggregate the calculated solar values given
by the raster to an area that is specified by a polygon of the footprint
shapefile. 

At the end I want to have one average number of incoming solar irradiance
per sqm for each footprint.

I hope you all can understand what I mean??

- I was thinking about to use r.to.vect to create a point file out of the
raster. 
- Then I thought about using v.select, to get only these points that are
inside of the polygons. 
- After doing that I could use v.overlay to extract only those points that
are within a specific polygon (in this case footprint). This step has to be
done for each polygon and that means to get a point file for each
footprint-polygon. 
- Then I could calculate the average value of each point cloud using Open
Office (access to .dbf file).

So I guess my proposed workflow is a little bit inconvenient... And I hope
that someone of you can tell me an easier way of doing that.

Thanks in advance,
Tim

 

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