Extracting smaller raster images from big ones

GRASS GRASS user
1

Help! I don't know if this is an obvious question, but I have been
searching the Grass manual and can't find an answer - I have large raster
images and want to extract smaller ones from them for the purpose of
supervised classification. How do I do this? I have the coords of the
smaller images I want. Defining smaller regions doesn't help, since
i.class doesn't take a region name, it simply loads the entire image !
Please help.... I don't want to export to IDRISI, then extract, and then
reimport, as that would take rtoo much time.
Thanks a lot
Harini

------------------------------------------------------------------------
| Harini Nagendra E-MAIL : harini@ces.iisc.ernet.in |
| Center for Ecological PHONE : 91 80 309 2639 (Hostel: LR-94)|
| Sciences : 91 80 309 2506 (Department) |
| Indian Institute of Science FAX : 91 80 334 1683 |
| Bangalore 560 012 India TELEX : 845 8349 IISc IN |
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2

I hope I have understood your problem correctly.

Couldn't you simply
1- set the region to whatever you want
2- r.mapcalc "small_raster=big_raster"
3- i.class on small_raster ?

then you can r.patch all your small rasters back together.

Cheers,

--
      Andrea Giacomelli
      andreag@idra6.iar.polimi.it
      http://idra6.iar.polimi.it:8080/~andreag
      tel: +39-2-23996233 fax: +39-2-23996207

3

Change your region to reflect the geographic boundaries and cell
resolution that you want, and then use r.resample. Piece of cake!
  -Malcolm

On Thu, 10
Oct 1996, Harini Nagendra wrote:

Help! I don't know if this is an obvious question, but I have been
searching the Grass manual and can't find an answer - I have large raster
images and want to extract smaller ones from them for the purpose of
supervised classification. How do I do this? I have the coords of the
smaller images I want. Defining smaller regions doesn't help, since
i.class doesn't take a region name, it simply loads the entire image !
Please help.... I don't want to export to IDRISI, then extract, and then
reimport, as that would take rtoo much time.
Thanks a lot
Harini

------------------------------------------------------------------------
| Harini Nagendra E-MAIL : harini@ces.iisc.ernet.in |
| Center for Ecological PHONE : 91 80 309 2639 (Hostel: LR-94)|
| Sciences : 91 80 309 2506 (Department) |
| Indian Institute of Science FAX : 91 80 334 1683 |
| Bangalore 560 012 India TELEX : 845 8349 IISc IN |
------------------------------------------------------------------------