[GRASS-user] no nulls outside project map area

William Kyngesburye woklist at kyngchaos.com
Fri Jun 5 20:10:20 EDT 2009

I'm an idiot.  It was the r.mapcalc in my script that wasn't taking  
nulls into account.

On Jun 5, 2009, at 3:52 PM, William Kyngesburye wrote:

> Ugh - tried it with GRASS 6.4 and I get the nulls.  Looks like a  
> GRASS 6.5 bug.
> On Jun 5, 2009, at 3:43 PM, William Kyngesburye wrote:
>> I started with a tiff image, in Albers projection.  Imported in a  
>> new location in GRASS - the tiff region is rectangular with no  
>> nulls in the region, so the GRASS region follows the tiff region  
>> exactly.
>> Then I projected to a latlong location.  The tiff is off to one  
>> side of the central meridian, so the projected image appears  
>> rotated and stretched, as expected:
>> <unprojected.png>
>> But the the triangular areas outside the original tiff region are  
>> white, not null.  My latlong region is larger than the image - I'm  
>> going to merge multiple tiled and overlapping tiffs - and there are  
>> nulls outside the extents of the projected area of the image.
>> Is this expected behavior?  I usually go from latlong to projected  
>> location, and the source latlong region is larger than the  
>> projected region so I don't see this.
>> GRASS 6.5svn

William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>

"History is an illusion caused by the passage of time, and time is an  
illusion caused by the passage of history."

- Hitchhiker's Guide to the Galaxy

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