[GRASSLIST:7174] Re: Gettting off the ground with v.surf.rst

Andrew Danner adanner at cs.duke.edu
Wed Jun 15 15:41:44 EDT 2005


 Some of your parameters seem a bit odd, mainly dmin, segmax, and npmin
seem way too high. What is your grid resolution from g.region -p?
Typically dmin is set to be 1/2 of the grid resolution so if you want a
20 meter resolution surface, try a dmin of 10. Decreasing dmin typically
increases the number of points used for the interpolation. Since your
dmin is high and your point count is low, I would look into adjusting
dmin first. 

 Once you fix that though, you may find that the interpolation step
takes forever, mostly because segmax and npmin are set quite high as
well. For LIDAR data from NCfloodmaps or LDART I typically use npmin=100
and segmax=20. The running time of the interpolation is roughly
proportional to (n/segmax)*npmin^3, so cutting both npmin and segmax in
half makes the program run about 4 times faster. 

 See if that helps. 


On Wed, 2005-06-15 at 14:52 -0400, Thomas Colson wrote:
> this may appear to be a stupid question, but I'm having a hard time
> getting the "desired" output from v.surf.rst, and I don't want to run
> downstairs and bother Dr. Mitasova with such a menial question....
> I have a x,y,z vector of LIDAR elevation data, and I'm trying to get a
> raster elevation surface based on the z col. I've tried many different
> variations of the output below, with the same errors "The number of points
> being used is 3
> " and so forth. I'm sure this has been done many times by someone in the
> know, any chance of an example command syntax so I can get this running?
> Thanks.
> v.surf.rst input=lidar3 layer=0 zcolumn=flt1 dmax=100000 dmin=10000
> elev=surf7 zmult=1.0 tension=40. smooth=0.1 segmax=400 npmin=2000
> Authors: original version -  H.Mitasova, L.Mitas, I. Kosinovsky, D.P. Gerdes
> See manual pages for reference and publications T3
> Percent complete: Reading lines from vector map ...
> Reading nodes from vector map ...
> Warning: strip exists with insufficient data
> Warning: ignoring 348352 points -- too dense
> WARNING: 3 points given for interpolation (after thinning) is less than
> given NPMIN=2000
> Warning : there is less than 2050 points for interpolation, no
> segmentation is necessary, to run the program faster, set segmax=2050 (see
> manual)
> The number of points from vector file is 348355
> The number of points outside of region 0
> The number of points being used is 3
> Processing all selected output files
> will require 1612 bytes of disk space for temp files
> Percent complete:
> history initiated

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