[GRASS-user] Spatially/networked constrained interpolation

[Jonathan Greenberg]

One of the issues we are currently working on (and the reason for the
barrage of emails about point files and whatnot) is moving towards
interpolating data which is located in a river network.  Are there any
spatial interpolation techniques available in grass which will take into
account "barriers" when calculating distances (say, if we are using a
kriging approach).  For instance:


----?-------
		\____X1_______
		/
---X2-------

These are two rivers flowing into a larger channel.  ? is an unknown value I
want to predict.  X1 and X2 are two stations that I have data for.  X2 is
geographically closer to ? than X1, but if you approach this viewing it as a
network or a costdistance surface where the distances must be constrained by
channel connectivity, X1 is closer than X2.  Initially I've considered
generating a costdistance surface PER station using a mask of the rivers,
and using that to figure out the distance of any arbitrary point to every
station, then pulling out the variogram info into R or some stats package,
make a model, then apply it to the stack of distance from station X rasters.
Is there a better way of doing this?

--j

--
Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N 
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307
MSN: jgrn307 at hotmail.com