[postgis-users] Reprojecting a PostGIS database

[Dylan Beaudette]

Hi Reid,

We have a mapserver application pulling data out of a PostGIS DB for CA, AZ, 
and NV. In our case, *area* is the important parameter we are trying to 
preserve, with *shape* being the second most important. Therefore an 
equal-area projection like AEA was our first choice. If you are trying to 
preserve angle (shape) over a large area (like the continental US) then a 
conformal projection like Lambert conformal conic might be a good starting 
point.

Since our specific projection was not in the SRS table, we added a custom 
entry, and projected our source data into the new SRS. As we rarely need the 
data in an alternate coordinate system, leaving our geometry in AEA made the 
most sense.

Cheers,

Dylan

PS: for projection on the fly use the transform(GEOM, SRID) function.

On Monday 05 February 2007 12:16, Reid Priedhorsky wrote:
> Hi folks,
>
> I have a PostGIS database which is currently in a Plate Carree
> projection (EPSG 4326); this looks significantly distorted, and so we'd
> like to change the projection we show to users to something less
> distortionary. This brings up two questions:
>
> 1. Is it better to reproject the database once and for all, or to leave
> it in 4326 and reproject on the fly? If the former, how can I do that?
>
> 2. How does one intelligently choose a projection from the thousands
> stored in spatial_ref_sys? Currently, we've got data from only the
> Minneapolis-St. Paul metro area and have no plans to expand, but we
> could grow beyond that eventually. Also, it would be nice if map units
> stayed within the range (-180, 180) which would allow us to minimize
> changes to other parts of our application.
>
> Any help, pointers to resources, or suggestions would be very much
> appreciated.
>
> Thanks,
>
> Reid
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-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341