[MetaCRS] failed epsg wkt (geotools)

[Martin Desruisseaux]

Christopher Schmidt a écrit :
> Ah, okay. So the org.geotools.referencing.CRS.decode() function is not
> yet in that code? THat's the only function I'm using so far :) 

Right, and this is the function I hope to bring back in January.

>> The above works for many cases, but of course not always. The proposed
>> improvement is to take the area of validity in account. Most Projected CRS
>> defined in the EPSG database have an area of validity. We could search for a
>> TOWGS84 element having an area of validity that contains the ProjectedCRS area
>> of validity.
> 
> Gotcha. Do you have a feeling as to whether there are cases where even
> that will fail? I'm curious as to whether, in the end, we're really
> going to be able to have "one true" WKT for a given projection, or if
> there are multiple "Best answers"...

I don't know yet. But my assumption is that there is many answers when asking
for a GeographicCRS (because those CRS are often based on Datum applicable to
the whole Earth, like WGS84, International 1924, etc.), but I would expect the
amount of answers to do down to one when asking for a ProjectedCRS (because
those CRS are often defined for a particular country).

We could apply Frank's rule of not providing any TOWGS84 when there is more than
one answer, with the modification of couting the amount of answer only after we
have filtered for deprecation, superseed and area of validity. I would expect
the end result to be no unique TOWGS84 for GeographicCRS, but unique TOWGS84 for
ProjectedCRS.


> For me, the EPSG database is a bit of a bear to trawl through, so
> perhaps this is an easy answer I just don't know. (I suppose if I had MS
> Access, it might not be as terrible; perhaps someone has built UIs into
> the access DB to make moving through it less painful.)

When thing that I would really appreciate would be a volunter creating a set of
OpenOffice.org forms for the EPSG database (using a connection to a PostgreSQL
database). Such volunter doesn't need to be a developper and would give us the
same browsing facilities than MS-Access users.

	Regards,

		Martin