[Gdal-dev] RE: [postgis-users] Adding to Spatial Ref Sys table

[Craig Miller]

Note:  This thread started on the postgis list.  I moved it here since this
tangent is gdal specific.

Frank,

It appears the the pg driver uses the wkt definition primarily in the
FetchSRSId method.  It would be trivial to just add the proj definition
along with the wkt definition in this section.  I'll take a look at it
tomorrow, add it, and submit the code along with the bug.

Thanks for the quick reply btw.  :-)
Craig

 

-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Frank
Warmerdam
Sent: Wednesday, March 29, 2006 5:09 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Adding to Spatial Ref Sys table

Craig Miller wrote:
> What is the "correct" way to add SRS definitions to the 
> spatial_ref_sys table.
> 
> I noticed that ogr only inserts the srid and srtext fields.  Are the 
> other fields required?  If they aren't required what is the proj4text 
> field used for.  Does it just improve performance by removing the need 
> to determine the
> proj4 string from the wkt string on the fly?

Craig,

As far as I know the WKT is just informative, and the proj4text is what is
actually used.  The OGR PG driver should be inserting the proj4text.
Without it the SRS creation option in the OGR PG driver is basically
useless.

If you file a bug on this, I'll try and get it fixed.

> I'm assuming that by populating the auth_name and auth_srid columns 
> that I can essentially define a "shortcut" to my any new definitions 
> that are created.  E.g. I could specify SPATIALMINDS as the authority, 
> and start numbering SRS definitions at 1 and refer to it as 
> SPATIALMINDS:1 just like I refer to EPSG:4329 in various places.

My take on this is that you should leave the auth_name and auth_srid blank
if the coordinate system isn't from EPSG or another standard authoritative
source.

Best regards,
-- 
---------------------------------------+--------------------------------
---------------------------------------+------
I set the clouds in motion - turn up   | Frank Warmerdam,
warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGF, http://osgeo.org

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