[GRASS-user] newbie category question..

GRASS GRASS user
,
1

Hi -

I'm trying to do something I thought was fairly simple, but eludes me...

I'm trying to find the average elevation of polygons. I used
gdal_rasterize to make a layer, which does indeed have unique categories,
and values, for each building.

I'm trying to use this layer against a DEM, and on a per-polygon basis,
get the min/max of the DEM ... I was thinking that somehow I might use
r.statistics, but....not so straightforward, apparently.

thanks in advance for any suggestions!

Chris

p.s. - it would sure be nice if I could make key/value pairs within
mapcalc; that way I could read a category from one layer, make a key, and
fetch it anywhere within mapcalc...

2

On Mon, 2008-03-10 at 15:50 -0700, cgnicholas@alamedanet.net wrote:

Hi -

Hi Chris!

I'm trying to do something I thought was fairly simple, but eludes me...

it took me a while till I understand how to do what other people told
me... on a similar problem. But since then I know where to look at
least :wink:

I'm trying to find the average elevation of polygons.

Try with v.rast.stats

or with

"starspan" which is created to handle raster vs vector statistical
problems like the one you have. Have a look at the user guide of it:
http://starspan.casil.ucdavis.edu/doku/doku.php?id=userguide

I used
gdal_rasterize to make a layer, which does indeed have unique categories,
and values, for each building.

I'm trying to use this layer against a DEM, and on a per-polygon basis,
get the min/max of the DEM ... I was thinking that somehow I might use
r.statistics, but....not so straightforward, apparently.

thanks in advance for any suggestions!

Chris

Cheers,

Nikos

p.s. - it would sure be nice if I could make key/value pairs within
mapcalc; that way I could read a category from one layer, make a key, and
fetch it anywhere within mapcalc...

I don't understand here.

_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

3

Try with v.rast.stats

exactly what I was looking for; thanks! (it is slowly crunching away...);
looks like it is a wrapper around successive r.mapcalc runs?

Have a look at the user guide of it:
http://starspan.casil.ucdavis.edu/doku/doku.php?id=userguide

Looks very cool! I'll admit in advance my response to the following might
be completely lame by comparison...

p.s. - it would sure be nice if I could make key/value pairs within
mapcalc; that way I could read a category from one layer, make a key,
and fetch it anywhere within mapcalc...

I don't understand here.

Just thinking if mapcalc, instead of just defining new map layers
(A=foo@mapset1...) you might use one layer as a Key for intermediate,
category-based running results in memory...but again, I will look at
starspan...thanks!

Chris