[WMS] Support arbitrary SRS codes (e.g. MOON:1) in WMS

[dmorissette]

Jeff DLB wrote asking if it would be possible to modify MapServer to support
arbitrary SRS codes in WMS, such as MOON:1.

Here is a summary of the email exchange:


Jeff de La Beaujardiere wrote:
> 
> Daniel Morissette wrote:
> 
>> Are you just looking for a way to pass an arbitrary WMS projection 
>> code without any real PROJ definition? If you don't expect MapServer 
>> to be able to "understand" the MOON:1 projection and reproject data 
>> to/from it, then I'd have to check, but it might not be too hard to 
>> modify the code to just do nothing if you pass it a SRS that is listed 
>> in the "wms_srs" metadata for the server and that doesn't have a valid 
>> PROJ definition.
> 
> 
> Short term, that would be okay. I thought I would modify mapwms.c to 
> accept my custom CRS id without complaint. Perhaps I must also set 
> map->units to an integer value of meters/degree on the moon?
> 
> Longer term, that hack would not be good enough to fold back into the 
> master source, and I would not wish to keep rehacking whenever mapserv 
> is upgraded. A way to define a new CRS in the PROJECTION section of the 
> map file would be nice. Something like this:
> 
> PROJECTION
>   "proj=moon:1"
>   "shape=spheroid"
>   "radius=1738000"
>   "flattening=3234.93"
> END
> 


Frank Warmerdam wrote:
> On Wed, 16 Feb 2005 10:26:43 -0500, Jeff de La Beaujardiere
> <xxxx> wrote:
> 
>>>Short answer: no you won't be able to convince mapserver to accept
>>>MOON:1 without touching the source.
>>
>>That's what I suspected from my investigations yesterday.
> 
> 
> Jeff, 
> 
> I would add that it is pretty easy to make a "fake" CRS in the EPSG name space
> if you were willing to settle for that. 
> 
> 
>>Longer term, that hack would not be good enough to fold back into the
>>master source, and I would not wish to keep rehacking whenever mapserv
>>is upgraded. A way to define a new CRS in the PROJECTION section of the
>>map file would be nice. Something like this:
>>
>>PROJECTION
>>   "proj=moon:1"
>>   "shape=spheroid"
>>   "radius=1738000"
>>   "flattening=3234.93"
>>END
> 
> 
> You can define a new projection using normal PROJ.4 parameters, including
> ones with unusual (aka non-earth) ellipsoids.  However, the hole is still allow
> that to be related to the SRS in WMS requests.  Currently there is an implicit
> special support for the EPSG name space, and for lookup it is mapped to the
> /usr/local/share/proj/epsg lookup file. 
> 
> I suspect what we need to do is allow a mapfile declaration of a list of
> "CRS lookup files" that would give the name of the file, and the proper name
> for the CRS namespace.  Then these would be allowed through in the various
> appropriate places. 
> 
> This isn't a trivial change, but I think it may be helpful as we start looking
> at new required CRS namespaces.   Of course, the AUTO projections would
> still have to be a programmatic hack. 
> 
> I would suggest that a bugzilla enhancement request be opened on this
> issue.  Feel free to add me to the cc: list.  If we had a good understanding
> of what needs to be done we could even implement it in time for 4.6. 
>

[dmorissette]

Definitely not in 5.0... setting target milestone to FUTURE.