[GRASSLIST:2894] Re: unwanted map borders

[Zbigniew Perski]

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.
> 
Kirk,
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.

Zbigniew

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



> 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
> ------------------------------------------------------------------------
>