Wolfgang:
There may well be a way to detect point-in-polygon in GRASS;
there definitely is a way to do so in R (which interfaces to GRASS):
Check out this example on our Web site:
http://nceas.ucsb.edu/scicomp/GISSeminar/UseCases/PointInPolygonAnalysis/point_in_poly.html
http://nceas.ucsb.edu/scicomp/GISSeminar/UseCases/PolygonOverlay/PolygonOverlay.html
You could exploit R calls within GRASS using the R spgrass6 package.
The above site has good introductory material and references for R,
Or check the R home page: http://cran.r-project.org
Regards,
Rick Reeves
--
Rick Reeves
Scientific Programmer / Analyst
National Center for Ecological Analysis and Synthesis
UC Santa Barbara
reeves@nceas.ucsb.edu
www.nceas.ucsb.edu
805 892 2533