Benjamin wrote: > A bit of web searching for "Interpolation Distance Weight" or > "Exponential Interpolation" (i.e. related to GIS and spatial > interpolation). did not produce anything meaningful for me. > Could you point me to some literature where I can find > more information on this?
do a search for "radial basis functions". e.g. a quick visit google finds: http://en.wikipedia.org/wiki/Radial_basis_function http://www.cs.ualberta.ca/~sutton/book/8/node7.html http://www.ncgia.ucsb.edu/conf/SANTA_FE_CD-ROM/sf_papers/fogel_david/santafe.html my knowledge of it is mostly from its application to interpolating 2 or 3 coupled-component velocity vectors between sampling sites. e.g. this from the Journal of Geophysical Research Sept 2006: http://www.otago.ac.nz/marinescience/po/pdfs/VennellBeatsonADCPtidalRBF2006preprint.pdf you can play with some simple decay function variations in the v.surf.icw and r.surf.volcano scripts in wiki addons. e.g. 1/d^2 gives better transitions for interpolations, but 1/d^3 better deals with minimizing errors due to unconstrained boundaries for extrapolations. IMHO the well known meaning of the "IDW" acronym shouldn't be changed by us as people may try a search for the known meaning. Augmented, well have fun, especially if you can cite a validation in the literature. Personally my main hope for GRASS in this area is to see the segmentation code improved in the RST modules so that the "block effect" in areas of high point-density gradient can be automatically tuned away. ie. for most situations why worry much about simple IDW when you have a much more advanced thin plate spline solution already there as a drop-in replacement? oh yeah, and update r.surf.contour from its current GRASS 4-era level. (0 elev in input data is treated as null; integer-only output) Hamish _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev
