[GRASSLIST:5807] s.surf.rst versus the impenetrable wall

[H Bowman]

Hi all - 

two questions regarding s.surf.rst:

1) Is it appropriate to use s.surf.rst for non-topographic data? eg pH
or some other continuously distributed parameter. I think it's ok, but
would like to be sure.


2) Does anyone have any ideas or insights regarding how to stop
s.surf.rst from interpolating over impenetrable barriers? Unfortunately
it is necessary for us to interpolate over a large distances with only a
few data points.

Setting a null mask just stops the values from being included in the
map, not from it including the interpolation over the null area. I guess
there is little that can be done in this regard, as we need to get
around corners etc.

Calculating for each region, patching together, and smoothing the
boundary isn't totally appropriate; the best I can come up with is do
one section (say sub-sample with r.mask.points), run s.surf.srt, use
r.random to randomly sample many sites from the new raster, and then add
the sites from the other half and re-run s.surf.rst for all.

Could using heavily weighted per-site-smoothing with smatt= help?

to see the problem:
http://bambi.otago.ac.nz/hamish/bad_interp.png
(interpolation jumping between waterways)


thanks a lot,
Hamish