[postgis] The SPATIAL_REF_SYS table

Roderick A. Anderson raanders at tincan.org
Fri Sep 21 09:52:42 PDT 2001

I've got PostGIS installed and stayed up far too late last night
starting to play.  Since I'm a GIS groupie (verses a real user) I'm
doing a bit of fumbling around understanding some of the concepts.

My plan is to have a seamless database of GIS/Mapping data of a fairly
large area.  I currently have about 180 USGS Quads of data for my area
with coordinates in UTM Zone 11N and some UTM Zone 12N (See question 3
below for why I think this is significant).  Coords and elevations are
in meters.  This is in case you haven't had the joy of using these files
while working in a feet and mile country.

To make the data loading easier I'm playing with the DEM data (x, y, z).
I have a perl script that transforms from the USGS DEM format to a
PostgreSQL copy'able format.

So I have three general questions.

1. What is (should be) the difference in the values of the columns SRID 
   and AUTH_SRID in the SPATIAL_REF_SYS table?

2. Does my table design make sense?  The idea being I can select a
   random rectangle of elevations or the points for a range of

	gistest=> \d elevation_pnt 
	      Table "elevation_pnt"
	 Attribute |   Type   | Modifier 
	 elevation | bigint   | 
	 pnt       | geometry | 
	Indices: elevation_pnt_elev_idx,
	Constraints: (srid(pnt) = 26711)
	             (geometrytype(pnt) = 'POINT'::text)

3. Can I have more than one SRID in this table?  If so how do I change
   the constraints to allow this?

                      Let Accuracy Triumph Over Victory

                                                       Zetetic Institute
                                                        "David's Sling"
                                                         Marc Stiegler

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