[GRASSLIST:8304] Re: Setting Null Values

[Ian MacMillan]

Dave, I am not sure if this is the way you want to do this, but you can 
draw a mask (r.digit) around the part of your map that is data, and set 
everything else in the region to null with r.null.  Then remove the 
mask and use r.patch.  You can't really automate this easily, but it 
should work.

-Ian


On Sep 15, 2005, at 8:47 PM, Dave Kent wrote:

> Hi:
>
> I have some scanned topographic maps in geotiff format.  When I try to 
> import them, r.in.gdal tells me that they are not orthogonal and I 
> need to straighten them with gdalwarp.   This works fine but as the 
> map is rotated,  I get black slivers along the edges of the maps.
>
> I want to patch the maps together.  If I set the black slivers to NULL 
> with r.patch -z or r.null the valid black content in the map 
> disappears as well.
>
> Is there a way I can use the -dstnodata feature of gdalwarp to set the 
> 'nodata' portions of the output map directly to a NULL value that 
> grass will recognize on input?
>
> Or is there some other way to solve this problem?
>
> Thanks for your help.
>
> Dave
>
>
 >
 >
What happens if a big asteroid hits Earth? Judging from realistic 
simulations involving a sledge hammer and a common laboratory frog, we 
can assume it will be pretty bad.
  - Dave Barry


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