[R] finding euclidean proximate points in two datasets

Alexander Shenkin ashenkin at ufl.edu
Thu May 20 16:02:46 CEST 2010

Hello all,

I've been pouring through the various spatial packages, but haven't come
across the right thing yet.

Given a set of points in 2-d space X, i'm trying to find the subset of
points in Y proximate to each point in X.  Furthermore, the proximity
threshold of each point in X differs (X$threshold).  I've constructed
this myself already, but it's horrificly slow with a dataset of 40k+
points in one set, and a 700 in the other.

A very inefficient example of what I'm looking for:

    for (pt in X$idx) {
        proximity[i] = euclidian_dist(X[pt]$x, X[pt]$y, Y$x, Y$y) <
	i = i+1

Perhaps crossdist() in spatstat is what I should use, and then code a
comparison with X$threshold after the cross-distances are computed.
However, I was wondering if there was another tool I should be
considering.  Any and all thoughts are very welcome.  Thanks in advance.

Alexander Shenkin
PhD Candidate
School of Natural Resources and Environment
University of Florida


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