PostGIS, geometry columns, and UTM.. I'm not sure where they are wrt
adding KNN support, but it's something they've been anxious to have for
a while, so I expect support will come quickly.
I've looked into this a little more.

One approach seems to be to project the lat/long pairs on to a flat
plane using the Albers projection (which would be a one-time
calculation), and then the current KNN point/distance calculations could
be used.

Here's a Perl module that references the Albers projection (although
it's not yet clear to me how to use it):

http://search.cpan.org/dist/PDL/

And a Wikipedia page on various calculation possibilities:
http://en.wikipedia.org/wiki/Geographical_distance#Flat-surface_formulae

Further suggestions welcome.

Thanks,

Mark

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