[GRASSLIST:2894] Re: unwanted map borders

Zbigniew Perski perski at us.edu.pl
Wed Mar 10 13:03:58 EST 2004

W liście z śro, 10-03-2004, godz. 15:54, Kirk R. Wythers pisze: 
> Which command cuts off "clips" unwanted map borders? I have a series of 
> scanned and rectified images (essentially tiles) that I intend to use 
> r.patch to combine into a single large map. However, there are borders 
> around each that needs to be removed before r.patch is applied.
some weeks ago I had the same problem I solved it in a very simple way:
1. Draw polygon arround the part of map which you want to have
2. Assign a label = 1 for the polygon
3. Rasterize the polygon wit region settings the same as for your map
4. Your new raster: "mask" map will have value 1 for the wanted area and
NaN for unwanted areas
5. Multiply your map with "mask" using mapcalc. For pixels with 1 from
the "mask" the resulted map will have oryginal values but outside the
porgram will assign NaNs

Of course you need a bit of work with digitizing  but with this method
you are able to cut even the irregular area.


dr. Zbigniew Perski
Geological Visualization Laboratory
Dept. of Fundamental Geology, Faculty of Earth Sciences
University of Silesia

> Thanks,
> Kirk
> ------------------------------------------------------------------------
> Kirk R. Wythers	                                     tel: 612.625.2261
> Dept. of Forest Resources                 fax: 612.625.5212
> University of Minnesota      email: kwythers at umn.edu
> ------------------------------------------------------------------------

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