Helena Mitasova helena at gis.uiuc.edu
Mon Mar 25 07:00:00 EST 1996

>One of my users recently  started (or trying) using the
>alpha/garden routine s.surf.tps.  At least on our site,
>this routine is worse than useless.  My users first attempt
>was on a fairly large data set (20,000 points: combine trajectory
>data), and the only response was floating point exception.
>Working with small data sets (less than 400 points), with no
>mask file, I can get s.surf.tps to ``surface'' 1, 2, 3, or 6
>data points out of 347.  All other points are ignored for
>being out of the region (even thought the site list file
>shows them to be in the region).  If I somehow stumble across a
>set of parameters (dmin, tension, smooth, segmax, npmin) that
>will surface through 6 points, and immediately re-run s.surf.tps
>with EXACTLY the same parameters, it only surfaces through 3 points.
>This seems likely to be a problem of using some value somewhere
>in s.surf.tps BEFORE it is set.

Has anybody used s.surf.tps with this version of GRASS?
Do you get any warnings or error messages from
the program, have you checked your region and resolution properly
(run d.sites with the same region you are using when running
as well as the format of your site data? (it should be x|y|#z, but
if it is not, you should get warning from the program).
The selection of points which are taken for the interpolation is completely
controled by g.region. The program would remove the data points
within the given region if they are closer to each other than dmin,
but that would mean that your region has only couple of rows and
columns when you get only 6 points, so I guess that the problem
is in the region.
20,000 points shouldn't be a problem, the program was used  with
much larger data sets. Please send me everything what program writes
and if that is not enough I can try to run the program here
for your data subset with our version of s.surf.tps, just to make sure
that nobody has changed anything in s.surf.tps for the release
you are using.

Helena Mitasova
University of Illinois

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