[postgis-users] spatial_ref_sys

[Markus Schaber]

Hi, Trevor,

trevorw wrote:
> I'm working in Alberta which uses a modified Transverse Mercator
> projection (called 10TM) for provincial scale data.
> 
> AFAIK there is no entry in spatial_ref_sys to describe this projection.
> Is there some protocol by which an entry might be added to future
> versions of PostGIS and is there a recommended procedure for numbering
> my own entry to avoid conflicts with future versions?

Yes. Currently, PostGIS losely synchronizes from Proj, and the Proj team
losely synchronizes from the EPSG database, which is the best free
collection of such projections.

This also explains why currently all SRIDs are equivalent to the EPSG
srids, but there's no technical reason to not accept other reference
systems. That's what the "authority" and "auth_srid" fields in
spatial_ref_sys are for. It's advised to assign the SRID from one of the
private use ranges from the EPSG, however, to avoid conflicts with
future additions.

So please check whether the EPSG and Proj already have your coordinate
system, and if not, ask them to include it.

http://www.epsg.org/ should have download and contact information,
proj at lists.maptools.org is the appropriate List for proj.

When they both contain 10TM, we should ask Strk to update spatial_ref_sys.

> If I add my own following the format provided, I an import my data with
> the -s flag and it displays nicely in QGIS, which I assume indicates
> that it is functional and coordinate conversion, and other functions
> will operate properly. Right?

Yes, it works for all applications that get their SRF data from the
spatial_ref_sys table, including the postgis internal transform() functions.

There are some applications which have their own reference system
database, you have to update them separately.

Markus

-- 
Markus Schaber | Logical Tracking&Tracing International AG
Dipl. Inf.     | Software Development GIS

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