[GRASSLIST:6612] Re: surf.rst and segmax, npmin

Māris Nartišs maris.nartiss at gmail.com
Sun Apr 24 13:58:30 EDT 2005


Have You read http://www.ing.unitn.it/~grass/conferences/GRASS2002/proceedings/proceedings/pdfs/Cebecauer_Tomas.pdf

I use v.surf.rst (Grass 6.0.0) to create DTMs from isoline contour and
aditional point data. I use tension 35, smoothing 1, segmax 100 and
npmin 400 with good results. Segmentation lineas are visible only at
very undersampled areas. I will fix that by ading some points there
and then will be no problems.
Consider ading some points at areas where segmenation is visible.


On 4/23/05, Jose Gomez-Dans <jgomezdans at gmail.com> wrote:
> Hi!
> I am trying to interpolate a DEM from an quasi-regular grid of the
> region of interest (meaning that I have one data point per resolution
> cell, roughly). I am using s.surf.rst (I can't get the data into GRASS
> 6.0), and I have noticed that if you look at the slope aspect angle
> plot of the interpolated surface, the joining lines of the
> segmentation procedure are clearly visible in some areas. I am able to
> get rid of them by changing the npmin and segmax parameters (say,
> segmax=200 and npmin=1000 yields good results). This however, greatly
> slows computations, and these values are just trial and error, I don't
> really know what set of values will be optimal.
> The documentation mentions that if these lines are visible, npmin
> needs to be increased, but is there some "recipe" or idea as to the
> nature of these numbers?
> Thank you very much!
> Jose

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