s.surf.tps_bath

[Helena Mitasova]

Eric Grinaker asks:
>
>I am creating a sea-floor elevation model with s.surf.tps, the source
>data is from digitized bathymetry points labeled with there respective
>depths.  The resulting raster layer has "above zero" elevations that
>appear to be related to sharp drops in depth.  The small amount of
>documenation I have suggests increasing the tension, however, an increase
>great enough to level the "overshoots" results in my depth locations
>appearing as a "sink hole" on the ocean floor.  Any suggestions would
>be greatly appreciated:)

Go back to a lower tension and make sure you define some non-zero
smoothing (my guess 0.1) it reduces the overshoots significantly and
still preserves the topography. If you still get some"above zero"
values change them to zero using r.mapcalc (it will create a sharp edge
what may be appropriate.)

>Are there any net sources for s.surf.tps
>documentation?

just the manual page and articles in GRASSClippings (Surfaces and modeling)
(not available on net, but I can put it on moon).
However, I will be presenting a short tutorial on s.surf.tps at the upcoming 
conference on Integration of GIS and Environmental modeling.
I can put my notes which will be distributed there on moon, if there is 
enough interest.
We plan to prepare a tutorial, however, this is an alpha program and
 is still undergoing important changes and enhancements so we will write
it when it gets more stable.

Helena
helena at zorro.cecer.army.mil