Hallo JM,

the extraction of contour lines from an interpolated raster surface in 
GRASS is done with r.contour; the resulting vector file can of course be 
exported. However, the interpolation you want to do may be quite 
disappointing when you are using few data-points, especially if you're 
trying inverse distance methods (s.surf.idw and s.surf.idw2). You can try 
s.surf.tps to see if this comes up with a reasonable surface. If you 
really want to know what it's all about, get this book and spend some 
time reading the introductory chapters on estimation of spatially 
distributed data; by the time you reach the kriging chapters, you'll wish 
you'd never started...

* Edward H. Isaaks & R. Mohan Srivastava, 1989. 'An introduction to 
Applied Geostatistics'. Oxford University Press.

But Peter Burrough ('Principles of Geographical Information Systems', 
1986) provides a concise overview of interpolation techniques that may be 
easier to understand.

Good luck,

Philip Verhagen
-- 


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