surfaces

[Helena Mitasova]

Dear Grasshoppers, Grassusers and Grassprogrammers,

for those intersted in surface interpolation Irina
Kosinovsky has rewritten the s.surf.tps program
as a library of functions, which allows the grass
programers to make changes in interpolation more
easily and also to develop various versions of
interpolation with similar algorithmic structure as splines.
The alpha version of library (tested at CERL) is now
available on moon as interp_lib.shar.Z and it also
includes the documentation and new s.surf.tps
and v.surf.tps(the later allows you to interpolate
from digitized isolines without the need to transform them
to sites).The new programs also allow you to output the deviations
into site file so that you can see how much your data were smoothed
out (use s.univar to cumpute the stand. deviation etc.)
and you can also output the quadtree used for segmentation
as a vector file. See manual pages and documentation for
details on enhancements.

Regarding the questionss on what s.geom and v.geom does,
get the manual page it has some references and I will also ask
Roman Waupotich to send a brief description of the methods
used in his program to the list. Whoever is interested in
triangulations, please check it out and let us know what
functionality you need which is not included in these
programs. You can also use s.geom for creating a convex hull
of your site data, transform it to raster and then use it as
a mask when using s.surf.tps to avoid excessive extrapolation
Both programs are a very nice addition to GRASS, it is worth
trying it.

For those working on SGI  I put the demo on 2d,3d and 4d
interpolation and visualization of concentration of nitrogen
on moon as hela_baydemo.tar.Z (when unpacked it has 37Mb, so
make sure you have that much space available). You need to
have an SGI with movieplayer installed to run it.

We will put the new r.resample.tps, s.surf.3d and crossvalidation
programs on moon as soon as they are rewritten with the
interpolation library.

Enjoy the new stuff and if you don't like something, just let me
know 

Helena