[MAPSERVER-USERS] WMS server with non-EPSG SRS?

[Frank Warmerdam]

Neil Best wrote:
> 
> Frank Warmerdam-2 wrote:
>> The normal practice if you want a non-EPSG coordinate system to be usable
>> for WMS serving with MapServer is to just extend the epsg init file with
>> the definition.  Is this unacceptable for some reason?
>>
> 
> I have been reluctant to do this because:
> 
> 1)  I was concerned about tinkering with core software files in a production
> system, without any hard evidence that there was any chance for an
> end-to-end solution (see #3).  At the moment I don't have a segregated test
> bed where I can test the effect of such a change on my Mapserver application
> and guarantee no interruption.  Is it still true then that Mapserver won't
> even respect "init=esri:xxxxx"?  

Neil,

I believe you can use other init files in MapServer, but WMS EPSG SRS
codes will only be looked up in the epsg init file.  So for WMS purposes
the coordinate system has to be in the epsg init file.

> 2)  I would be extending a popular, mature standard in an ad hoc, maverick
> fashion (which is central to some business models, but not ours!), mainly
> because of the risk of future complications as the standard evolves and the
> maintenance overhead of propagating my amendments and remembering to reapply
> them any time that software is upgraded or new systems are provisioned.

Well, I would claim this is an implicit problem in the WMS standard
which (at least at 1.1) is tied to the assumption that EPSG is all
the coordinate systems anyone will ever need.

> 3)  I have no reason to expect that the client (ArcGIS Server in this case)
> will understand what it is that is being advertised, assuming that an
> analogous look-up table is contained somewhere within its WMS client
> implementation.  Is there any reason to think that Arc's WMS client relies
> on the proj support files that are included with the GDAL code that ships
> from ESRI?  Do I really want to get into the scenario of violating my
> customer's end user license or voiding their warantee by editing files
> installed by ESRI software?

Yes, well, that is certainly the other side of the problem. Arbitrary
extensions to the epsg code set are often not recognised by client software.

> On the other hand, it is useful to know that such an edit is considered a
> "normal practice" by someone I can trust to make such a judgment.  That
> said, is there anyone else who considers the standard unnecessarily
> constraining in this respect or am I shouting into the abyss?

Well, I'd claim you are shouting at the wrong people!

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 OSGeo, http://osgeo.org