Roger Bivand wrote:
Point-in-polygon functions are in the splancs package, but there you need the polygons.There's also nearest-neighbour functions in Splancs - the nn2d function returns the distances and indices of the nearest points in one set (the grid) to another set (the data points). 'Interpolation' is then just a matter of taking the value of the factor indexed by the result. Its easier to do than describe.
It is inefficient though, since it computes all Npts x Ngrid neighbour distances. Horrible if you want to do a large number of simulations, but if it takes twenty minutes and you only have to do it once, put the kettle on and have a cup of tea while the Computer Scientists tell you how to improve the algorithm. The function will be finished and your tea drunk by the time they've explained it.
There are functions in package spatstat too, for instance nearest.raster.point() does the reverse of what you want - which raster cells are nearest to point coordinates - not which are closer.Hopefully Rasp will have better point/polygon/nearest-neighbour functionality.
Please contact me off-list if I can help further.
I've emailed Matt the splancs-based solution.
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