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List:       postgis-users
Subject:    [postgis-users] Buffering advice
From:       galen () shackprices ! com
Date:       2007-03-31 0:49:03
Message-ID: 3891.207.254.98.148.1175302143.squirrel () webmail ! shackprices ! com
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I searched around and came upon an old discussion about buffering in
geographic coordinate systems -
http://postgis.refractions.net/pipermail/postgis-users/2005-May/007959.html

I'm hoping to buffer points and polygons across the USA and I'm looking
for a good-enough solution that will be reasonably accurate and will leave
me with circles that look like circles on Google Maps.

I have considered a few options:
1. Find a projection that adequately covers the US and run with it
(suggestions?).
2. Import a StatePlane boundary shapefile into PostGIS, project it to SRID
4269 (lat long). Then take a lat long point, check which StatePlane
polygon it falls within, project it to that projection, buffer, and
project the resulting polygon back to lat long.
3. Create a temporary TransverseMercator projection for every point and
buffer that, as suggested by Paul in the referenced conversation (if so,
any advice?).

I don't think number 1 is viable (but it sure would be nice!). 3 seems
somewhat over my head and 2 seems sloppy. 2 and 3 would still be stop-gap
solutions if I ever needed to sort polygons by distance from a point, at
least on the margins.

Sorry for the projection-newbie question. I understand GIS pretty well,
but I've never had to do deal with non-local projections.

Any advice?

Thanks,
Galen

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