dnorm is an average size of the segment (not window); so points that are
farther apart than dnorm + window size are computed independently.

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This is a GRASS 5.0 version of a program
for interpolation by regularized spline with tension.
The original version was implemented in GRASS4.1 as
s.surf.tps.
This version has been rewritten (see DESCRIPTION)
and numerous enhancements were added (see S_SURF_RST.html).

Original program was written by Lubos Mitas and Helena Mitasova.
GRASS4.1 implementation by Irina Kosinovsky and Dave Gerdes
Rewriting to floating point was done by Irina Kosinovsky 1995
Modification for new site format was done by Darrell McCauley 1995
Various enhancements including spatially
variable smoothing  were added by Lubos and Helena, 1997
Also, normalization of z was removed, so neither smoothing
nor z is normalized.

You must have the floating point patches, the new sites API,
the datetime API, and the TimeStamp patches to install these
programs.

The methods are described in (use these papers as references in
your publications):

    Mitasova, H., and  Mitas, L., 1993,
       Interpolation by Regularized Spline with Tension:
       I. Theory  and  implementation.  Mathematical Geology, 25, 641-55.

    Mitasova, H., and Hofierka, L., 1993
       Interpolation by Regularized Spline with Tension:
       II. Application to terrain modeling and surface geometry  analysis.
       Mathematical Geology, 25, 657-69.

    Mitasova, H., Mitas, L., Brown, W.M., Gerdes, D.P., Kosinovsky, I.,
       Baker, T., 1995, Modeling spatially and temporally
       distributed phenomena: New methods and tools for GRASS GIS.
       International Journal of Geographic Information Systems,9(4), 433-46.
