[MetaCRS] failed epsg wkt (geotools)

[Christopher Schmidt]

On Tue, Dec 16, 2008 at 12:59:18PM +0100, Martin Desruisseaux wrote:
> Mikael Rittri a écrit :
> > * EPSG:3388, Pulkovo 1942 / Caspian Sea Mercator
> > 
> > According to EPSG, the projection method is "Mercator (2SP)", coord op method 9805, 
> > with a standard parallel at 42°N.
> > But on SpatialReference.org, the projection method in OGC WKT is given as "Mercator_1SP", 
> > and the standard parallel is absent from the parameters.
> 
> Thanks for the note. Just for record and because Christopher reported testing
> GeoTools for an eventual usage in SpatialReference.org, I tested that GeoTools
> 2.x produces a WKT closer to the expected one, using "Mercator_2SP" projection
> and the correct standard parallel value. The output from GeoTools 2 is:

Martin,

Thanks. Right now, our WKT is based first on proj/geotiff/gdal, with a
fallback to Geotools when proj can't produce the correct WKT. Perhaps an
evaluation of whether this makes sense is in order :) Certainly, I
expect that as we attempt to act as a more up to date and official
reference, we're likely to turn up bugs in all the software we're using
to generate this WKT: Hopefully this is a positive for everyone :)

> PROJCS["Pulkovo 1942 / Caspian Sea Mercator",
>   GEOGCS["Pulkovo 1942",
>     DATUM["Pulkovo 1942",
>       SPHEROID["Krassowsky 1940", 6378245.0, 298.3, AUTHORITY["EPSG","7024"]],
>       TOWGS84[-40.595, -18.55, -69.339, 2.508, -1.832, 2.611, -0.8867324020562674],
>       AUTHORITY["EPSG","6284"]],
>     PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]],
>     UNIT["degree", 0.017453292519943295],
>     AXIS["Geodetic latitude", NORTH],
>     AXIS["Geodetic longitude", EAST],
>     AUTHORITY["EPSG","4284"]],
>   PROJECTION["Mercator (2SP)", AUTHORITY["EPSG","9805"]],
>   PARAMETER["standard_parallel_1", 42.0],
>   PARAMETER["latitude_of_origin", 0.0],
>   PARAMETER["central_meridian", 51.0],
>   PARAMETER["false_easting", 0.0],
>   PARAMETER["false_northing", 0.0],
>   UNIT["m", 1.0],
>   AXIS["Northing", NORTH],
>   AXIS["Easting", EAST],
>   AUTHORITY["EPSG","3388"]]
> 
> I also tested that it reports "Oblique_Mercator" (not "Hotine_Oblique_Mercator")
> for the 10 others reported issues.
> 
> However issues with GeoTools 2.x (to be adressed in geotidy/geotools 3):
> 
>   * Some parameter name in Geotools 2 are inacurate (for example
>     LambertAzimuthalEqualArea has a "longitude_of_center" instead
>     than the "central_meridian" used in most other projections).
>     This is already fixed in geotidy.

Is geotidy in a branch, or if I use the 2.6 development jar, do I get
the more correct/recent behavior? 

>   * The TOWGS84 string, will extracted from the EPSG database, are
>     not always the most appropriate one when EPSG defines many datum
>     shift for the same CRS. This is an issue I plan to fix soon.

How do you plan to fix this? As I understand it, these EPSG codes
actually have multiple 'correct' forms. This is on the plate for sr.org
to deal with as well, but not done yet. I believe that GDAL's approach
to this thus far has been to not export any WKT when there are multiple
correct ones (or something along those lines). (Note that all of my
comments on the proj/geotiff/gdal code are based on third hand
knowledge, so if they're wrong, I apologize ahead of time.) 

Regards,
-- 
Christopher Schmidt
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