[GRASS-dev] G7: v.loutlier Decomposition failed

Markus Metz markus.metz.giswork at gmail.com
Sun Dec 8 12:46:13 PST 2013

On Fri, Dec 6, 2013 at 1:17 PM, Blumentrath, Stefan
<Stefan.Blumentrath at nina.no> wrote:
> Hi
> Maybe it is not of importance, because no one else would use such extreme
> settings, but in case someone considers it as a bug:
> I was testing a bit with v.outlier in GRASS 7 on dense LiDAR data (~4 points
> per m2).
> When I use a very low Tykhonov regularization parameter (lambda_i) of
> 0.0000000000000000001 and rather short spline steps (1.5) at 0.5m resolution
> I get an error-message:
> “Decomposition failed at row 16499 and col 0”

I found similar errors with very small lambda values, i guess it's
some floating point precision limit. It seems that lambda should not
be much smaller than 0.0001. For v.outlier, I would leave lambda at
the default and rather use shorter spline steps, if you want to
fine-tune the results.

Markus M

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