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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