[GRASS-user] extract by attribute from a dem

[Charles Ehlschlaeger]

It is also possible that the region was not set to the geographic
coordinates of the dem or slope map when performing the r.mapcalc.
r.slope.aspect is one of the few programs to default to extent and
resolution of the original map, not the current region.

Chuck Ehlschlaeger, Associate Professor of Geography
Western  Illinois  University
215 Tillman Hall, 1 University Circle, Macomb, IL 61455
cre111 at wiu.edu, phone: 309-298-1841, fax: 309-298-3003


-----Original Message-----
From: grass-user-bounces at lists.osgeo.org
[mailto:grass-user-bounces at lists.osgeo.org] On Behalf Of Martin Landa
Sent: Wednesday, November 21, 2007 1:23 PM
To: nishith datta
Cc: GRASS users list
Subject: Re: [GRASS-user] extract by attribute from a dem

[please cc to grass-user ml...]

2007/11/21, nishith datta <nkdiitd2002 at gmail.com>:
> thanks for the prompt reply,
> sorry it didnot work either ?
> any ideas why ?
> can I somehow see the data in the raster layer - slope original. I mean
the
> count of pixels and the categories i.e the slope value against each
> category.

in spearfish

$ r.slope.aspect ele=elevation.dem slope=slope

$ r.stats slope nsteps=10 -c --q
0-5.252012 731997
5.252012-10.504024 775215
10.504024-15.756036 545337
15.756036-21.008047 335709
21.008047-26.260059 152262
26.260059-31.512071 56475
31.512071-36.764083 12735
36.764083-42.016095 1251
42.016095-47.268107 117
47.268107-52.520119 9
* 358245

$ r.mapcalc 'new=if( slope <= 20, slope, null())'

$ r.stats new nsteps=10 -c --q
0-1.999213 156159
1.999213-3.998426 346518
3.998426-5.997639 352206
5.997639-7.996851 314379
7.996851-9.996064 277200
9.996064-11.995277 237015
11.995277-13.99449 210267
13.99449-15.993703 178020
15.993703-17.992916 148995
17.992916-19.992128 270
* 748323

> may be there is something wrong with the slope map.
> Also won't changing 20 to 90 in the expression if(slopeoriginal <= 20,
> slopeoriginal, null()) give me the original map again?
> thanks
> nishith


-- 
Martin Landa <landa.martin at gmail.com> * http://gama.fsv.cvut.cz/~landa *
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