Markus and others,
I would like to say thank you for your regarding DTM interpolation with
v.surf.rst.
It worked fine for me using the following approach: I interpolated it
first with v.surf.rst, using a small tension value to get a smooth DTM.
This version contained the artefacts. Then I did r.random to generate 3d
points from the first result and finally did another v.surf.rst with the
default tension/smoothing values. This removed all the rectangular
artefacts.
My project was probably a stress test. I worked on a map of the
Kilimanjaro region with rather dense contours (from an older map) and
had to generate a 2m DTM for an area of 40 x 50km. For the full region
it interpolated for several hours (around 12 hours) but it finally
worked well. The result will be used in a new topographic map for
mountaineers in the Kilimanjaro region.
I can say that the results of v.surf.rst are much better compared to
what I can achieve with ESRI software. The TIN approach generated ugly
triangular artefacts and the topogrid method had ugly artefacts
perpendicular to the contour lines. And I couldn't fine-tune the
topogrid algorithm to get better results.
For v.surf.rst it took me a while to figure out the correct parameters.
There are a lot of settings that influence the results, but finally it
worked out fine.
Thank you very much for your help!
Andreas
Markus Neteler wrote:
Andreas,
here some older post from Helena (I have taken out non-relevant
comments, and it is now v.surf.rst):
On Thu, Jan 10, 2002 at 11:01:13AM -0500, Helena Mitasova wrote:
substantially reduce the number of
points on contours - they are oversampled (choose dmin at least 1.5 times
resolution and dmax a BIG number so that the program does not add
additional points to contours). If you still get the segments - run
r.random on your new DEM in the area where you have the visible segments
to generate few additional points and add them to your contours and
reinterpolate. And use smoothing at least 0.1 (you can use variable
smoothing with s.surf.rst - set it zero for the peaks and higher value for
the flat areas).
...
It is not too difficult to fix the visible segments problem - the errors
is very small so it is more cosmetics (but a very unpleasant one) - so
those segments just need to be smoothed out withing the program - we used
to have it with older segmentation that we used for the MG93 paper).
...
Helena
You also find this addressed in the new GRASS book (3rd edition).
Markus
--
--
Andreas Neumann
Böschacherstrasse 6
CH-8624 Grüt (Gossau ZH)
Switzerland
Phone: ++41-44-2736668
Email: [EMAIL PROTECTED]
Web: http://www.carto.net/neumann/
SVG Examples: http://www.carto.net/papers/svg/samples/
SVG.Open: http://www.svgopen.org/
_______________________________________________
grassuser mailing list
[email protected]
http://grass.itc.it/mailman/listinfo/grassuser
