[GRASS-user] Artefacts when interpolating DTM from Contour Lines with v.surf.rst

[Michael Barton]

In addition to Helen's advice, this also happens do to resolution issues.
Make sure that your computational region (set with g.region) matches the
resolution of the raster you are creating.

Michael


On 10/8/07 10:08 PM, "Andreas Neumann" <a.neumann at carto.net> wrote:

> yes, I am changing various values, including dmin. I get different sizes
> of the rectangular artefacts, but they never really disappear,
> regardless of the values I used. I still hope I can find a better
> parameter combination where the artefacts aren't visible.
> 
> Andreas
> 
> Andrea Ricci wrote:
>> Andreas Neumann wrote:
>>> Hello,
>>> 
>>> I am trying to interpolate a raster DTM from contour lines. I like the
>>> results from v.surf.rst, however, this algorithm, at least with my
>>> settings seams to generate rectangular artefacts in the resulting DTM.
>>> See
>>> a hillshade of my result at
>>> http://www.carto.net/neumann/temp/hs_dtm_tension5_smooth2.png - if it
>>> weren't for these artefacts I would like the results very much.
>>> 
>>> Here are the parameters I used:
>>> v.surf.rst input=hl layer=1 zcolumn=elev_m dmax=10 dmin=0.5
>>> elev=dtm_tension5_smooth2 zmult=1.0 tension=5 smooth=2 segmax=40
>>> npmin=300
>>> --overwrite
>>> 
>>> The idea is to get a smooth, not too detailed DTM, hence the small
>>> tension
>>> and higher smooth values.
>>> 
>>> Are there any parameters or postprocessing steps that would help me
>>> remove
>>> these rectangular artefacts? Or alternatively, are there better
>>> methods to
>>> interpolate DTMs from contour lines?
>>> 
>>> Thanks for any ideas,
>>> Andreas
>>> 
>>> 
>>>   
>> Try with increasing dmin= 2 or try with other values. Normally, in case
>> of visible segmentation, this value must be increased.
>> hope that's helpful
>> Andrea Ricci

__________________________________________
Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton