[STATSGRASS] questions regarding GRASS/gstat

[Thomas Adams]

I have been attempting to use gstat within GRASS and have had success up 
to a point. I am attempting to estimate precipitation over a large river 
basin (~450000 sq km) from monthly (not mean monthly) point values. I'm 
working with a Lambert Conic Conformal grid region with a ~5 km grid 
spacing (the x & y spacings are slightly different). My orginal dataset 
has nearly 500 data points, but some were too close together (actually 
coincident points with different IDs), so I wrote a program to eliminate 
points that were too close, <7.5 km. I have increased this threshold 
several times, to 50 km and still get a gstat error when I attempt the 
ordinary kriging, which says that I have a "matrix library error: 
singular matrix".

I must be doing something wrong since my once nearly 500 station 
locations is now ~100! One other note, is that gstat reports that some 
of my stations lie outside my mask region (the river basin boundary), 
but I don't see that this should be a problem, is it?

Also, I can run the Maas data example from the "Open Source GIS" book by 
Neteler & Mitasova without problems.

I am running GRASS 5.0.3 and gstat 2.4.3 on Linux.

Regards,
Tom

-- 
Thomas E Adams
National Weather Service
Ohio River Forecast Center
1901 South State Route 134
Wilmington, OH 45177

EMAIL:	thomas.adams at noaa.gov

VOICE:	937-383-0528
FAX:	937-383-0033