[postgis] The SPATIAL_REF_SYS table

Roderick A. Anderson raanders at tincan.org
Fri Sep 21 11:08:23 PDT 2001

On Fri, 21 Sep 2001, Paul Ramsey wrote:

> The Big List of EPSG SRIDs which Frank helped put together at
> http://www.opengis.org/techno/interop/EPSG2WKT.TXT is especially useful
> for filling out a SPATIAL_REF_SYS table. Note that the SRID number can
> be anything you like: it is local to your computer, unline the EPSG
> code, which is defined in the EPSG standard.

Grabbed it and loaded the UTM zone 11N tuple.

So using the AUTH_SRID for SRID would be OK on my virgin system.

> No, OpenGIS (correctly) expects you to store your features homogeneously
> with regard to spatial ref system. I am guessing that you want to store
> multiple UTM zone information in the same table? Bear in mind that when
> you do that, you are no longer storing things in a 'seamless tile'. It
> is like storing all your features in coordinates relative to the USGS
> quad they are in: sure, theoretically the data is seamless, but
> practically it is very hard to work with data which crosses the sheet
> lines. I'd suggest you find a nice planar projection which works for
> your entire working area, rather than messing with multiple UTM zones.

I had a feeling this was the way it was designed.  Since I have such
grandious plans I'll look at converting to a more seamless coordinate
system.  I'm going to have to dig out the old surveying and coordinate
geometry text books now.  LAT/LONG?  But I'm thinking - will the
selection functions (BOX3D etal.) work on spherical coordinates?
Probably not!

I'm sure the stuff I'm bringing up has been discussed many times in
other forums so please bear with me as I boot strap myself into the real
world of GIS and mapping.  Also tell me to shutup or pipe-down when it
gets to be too much.

Last thing.  Can anyone point me at readings on planetary level
coordinate systems?  8-|

                      Let Accuracy Triumph Over Victory

                                                       Zetetic Institute
                                                        "David's Sling"
                                                         Marc Stiegler

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