[bezema@lat-lon.de: Re: [martin.desruisseaux@geomatys.fr: Re:[MetaCRS] Introduction]]

[Frank Warmerdam]

Rutger Bezema wrote:
> I think Frank Warmerdam's point, that "...there are definitions EPSG doesn't
>  want to represent for good reasons", is valid. I believe it to be one of
> the reasons, that the creation and maintanance of one super crs library will
> be a project with lots of 'extreme timeconsuming' side effects, and with
> marginally gains. In my opinion the geotools and deegree approach to supply
> different file format readers, will --in the end-- keep the sub sets of
> databases managable without having to reinvent the wheel every time.
 >
> I believe a collection of such standardized 'Providers' would be most
> beneficial for all spatial referencing projects, independent of the
> programming language.

Rutger,

I'm afraid, I once again seem to be missing folks point.  I assumed the
Providers you were talking about were basically software to read definitions
in different formats, and return them in some normalized internal form
for your package but that doesn't jive with the providers being independent
of the programming language.

I am basically imagining us writing some tools to translate various
things into a nominal main format (perhaps a MetaCRS profile of GML CRS)
and then the various projects could convert this into their native
dictionary format.

This is roughly what I do now with EPSG definitions.  My current process
is:

1) Dump selected tables of interest from the EPSG database into .csv files
(within the libgeotiff respository).

2) Run some python scripts to build pcs.csv and gcs.csv files that basically
pull together all the information I need for a PCS or GCS into a single record
(including the TOWGS84 transform if one, and only one is available).  These
pcs.csv and gcs.csv files then go into the GDAL "data" directory.

3) Run the epsg_tr.py script to create a PROJ.4 init file, and a set of
spatial_ref_sys SQL insert statements for postgis.  I'm also working
on automated production of the QGIS "srs.db" file, which is roughly the
same as the spatial_ref_sys table from postgis, but as an sqlite database
file.  This script can also produce dumps in WKT and GML/XML format though
those aren't used systematically by anything at this time.

I also maintain a "esri_extra.wkt" file in the GDAL project which contains
the WKT definitions of a bunch of coordinate systems from ESRI using
code numbers outside the EPSG range.

I also maintain an ecw_cs.wkt file with WKT definitions for a bunch of
ERMapper/ECW coordinate system names.

I also maintain a cubewerx_extra.wkt file with WKT definitions for a bunch
of coordinate systems that are often used via pseudo-EPSG-codes for
WMS web mapping (mostly I get these from Cubewerx).

I also have an IAU2000.wkt which WKT coordinate system definitions for a
bunch of International Astronomial Union coordinate systems for other
planets and moons.

The OGRSpatialReference class knows how to consult all these files when
searching for a match for a user provided coordinate system.  But currently
these are not all uniformly available in PROJ.4, PostGIS or QGIS.  Also
the extensions are not available in GeoTIFF (though I don't think they
ought to since that is explicitly EPSG based).

What I'd like to do, is share the effort of maintaining dictionaries like
the ESRI, ERMapper, IAU and "other extra" dictionaries and to ensure they
are available for use in a reasonably consistent manner for the various
packages built on our software.

All this said, I'm really fine with putting off this dictionary management
discussion and effort for a bit till we get some core MetaCRS work done.

PS. I neglected to mention, I also maintain gt_datum.csv, and gt_ellipse.csv
with NIMA / GeoTrans definitions and gcs.override.csv and pcs.override.csv
files with some custom alterations/definitions for EPSG coordinate systems
(picking a particular towgs84 transformation for instance).

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