[GRASS-user] Raster Hole/NODATA filling programs

[William Kyngesburye]

On May 14, 2008, at 2:25 PM, Frank Warmerdam wrote:

> The r.fillnulls *appears* to scan the entire boundary of a nodata  
> area to
> build a point list of boundary values used for spline based  
> interpolation.
> I'm concerned this would not work well for situations like contour  
> data with
> large nodata areas or for situations where relatively sparse data has
> been applied to a raster and we need to interpolate from that (so  
> essentially
> most of the image might be one connected nodata area!).

Yeah, r.fillnulls has problems with large holes.  I used it on the  
SRTM data, and large holes get block anomalies, probably because of  
the SEGMAX (for v.surf.rst) used by r.fillnulls.  I played with that a  
bit in a customized r.fillnulls, but the bigger the SEGMAX the longer  
the processing, and it only helped a little.

>

I didn't pursue any further improvements to fillnulls, though I did  
experiment with filling at a coarser resolution, converting to points  
and using v.surf.rst with those as an enhancement to a similar process  
to r.fillnulls (it gave the full resolution v.surf.rst a little more  
interior meat to work from).  But I got distracted by "real" work and  
dropped the experiment.

-----
William Kyngesburye <kyngchaos*at*kyngchaos*dot*com>
http://www.kyngchaos.com/

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