[postgis-users] Which SRID to choose?

[Markus Schaber]

Hi,

On Thu, 25 Mar 2004 10:09:47 +0000
Homme Zwaagstra <hrz at geodata.soton.ac.uk> wrote:

> Your GPS receivers are likely to return coordinates in the WGS 1984
> system. The EPSG (http://www.epsg.org/) code for this is 4326. All
> srids currently appear to be the same as the EPSG code in the
> spatial_ref_sys table:
> 
> select srid,auth_srid from spatial_ref_sys where srid != auth_srid;
> 
> I can't comment much on your shapefile data except that shapefiles
> don't contain coordinate system information.  You therefore have to
> find this out from associated metadata or your data supplier. If this
> doesn't reveal a specific EPSG code then some judicial searching of
> the spatial_ref_sys table (based on the coordinate system parameters
> you have otherwise found) should be fruitful.

We learned that our shapefiles are in in WGS 1984, too.

While searching for the DE_DHDN / GK_3 System that one of our customers
used I stumbled over the following problem:

There seems to be some difference between the EPSG codes in PostGIS and
the actual EPSG data - when I look for the "Deutsches
Einheitsdreiecksnetz" in Postgis, I get the SRIDs/EPSG-IDs 31491 to
31495, while the current EPSG database defines 31461 to 31469. Most of
the other reference systems seem to match.

Did I compare the wrong columns, or where is my error?

Happy Easter,
Markus

-- 
markus schaber | dipl. informatiker
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