[postgis-users] Selecting geocoded postal codes within a given distance ( miles for example )

[Paul Ramsey]

In the curious world of UTM (and planar systems in general), the answer 
depends on where you are :)  Planar systems are local transforms which 
make a range of spherical lat/lon coordinates into a planar 
approximation. Because the world in spherical, it is very hard to have a 
planar projection which is covers a very large area, is true to shape, 
and is true to distance. So different parameterizatios of planar 
projections are used for different locations. If you are on the west 
coast of North America, then UTM10 (EPSG 26910) would be a good UTM 
projection. But if you are in Texas, then a different projection would 
be best.

Question number one when picking a planar projection is "how spatially 
big is your dataset?" Ie, what are its bounds in lat/lon?

Paul

Hugh W. O'Brien wrote:
> Thanks for the reply Paul.  I had come to the conclusion that I had 
> those 2 choice but wasn't sure which one was more difficult.  Thanks for 
> pointing out which one is easier to implement.
> 
> Now for a followup question?
> 
> What's the best way to convert my geocoded postal codes to UTM?
> 
> What would be the appropriate SRID of my new data set if I chose UTM as 
> my new rectangular cooridinate set?
> 

       __
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      | Paul Ramsey
      | Refractions Research
      | Email: pramsey at refractions.net
      | Phone: (250) 885-0632
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