Thanks, Jorge and Hamish for elaborating on this.
If I understand correctly, then Jorge's additions could be integrated
seamlessly into v.surf.idw, that is without breaking/changing its
default behaviour? If so, I am in favour of integrating these additions
into SVN.
I agree that we should stick with the established terminology. I think
the best we might be to extend the module description to something
like:
"Surface interpolation from vector point data by Inverse Distance
Squared Weighting and Radial Basis Functions" ???
Some additional details for the HTML man page would also be good.
Ben
Hamish wrote:
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
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Benjamin Ducke
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