[Gdal-dev] Proposed Feature: Consumption of URL-based Spatial References

Jan Hartmann j.l.h.hartmann at uva.nl
Tue Jul 24 09:17:41 EDT 2007

Completely off-topic of course, but I just realised that that Parisian 
meridian plays an important role in Dan Brown's "The Da Vinci Code". I 
forgot the details but it had something to do with the offspring of 
Jesus Christ. Anyway, Gdal seems to move into the realms of theology 
too. :-)


Jan Hartmann wrote:
> Yes, this is a good idea. I am working with historical maps with their 
> own projections (e.g. central meridian in Paris), and a central 
> repository for those definitions would be very welcome. One wish: it 
> would be nice to be able to name the projections, e.g. "Cassini" for the 
> 18th century French projection. Did you know BTW that our definition of 
> the meter as 1/40000 of the globe circumference comes from work done for 
> creating that projection?
> Jan
> Dr. J. Hartmann
> Department of Geography
> University of Amsterdam
> Howard Butler wrote:
>> All,
>> Chris Schmidt and I have been working on a website 
>> <http://spatialreference.org> that reflects the EPSG spatial reference 
>> codes database and user-contributed codes in a variety of output 
>> formats.  The EPSG code database is never as up to date as you would 
>> like, and we frequently tell people to hack their /usr/share/proj/epsg 
>> database file with made up codes to support alternative projections.  
>> If we could consume URL-based spatial references with OSR, all that 
>> would be required is someone adds the custom coordinate system 
>> definition to the site and then everyone could refer to it at that 
>> location (hopefully indefinitely).
>> As for the website itself, if it has uptake and people find it useful, 
>> we will work to put it somewhere it can live for a very long time -- 
>> for example OSGeo.  The source code (it's written in Django) will be 
>> made available so anyone can stand up their own version of the site.
>> I would like to propose that an ImportFromUrl() method be added to 
>> OSRSpatialReference that constructs a spatial reference given the 
>> SetFromUserInput data retrieved at the given URL.  It would only need 
>> to be as specific as that, and it wouldn't need to refer to 
>> spatialreference.org.  Additionally, this mechanism could be used to 
>> support GML SRS retrieval from URLs (which Frank mentioned was in the 
>> spec) in the future.  This method would only be active if you have 
>> included curl support, of course.  Maybe someday, if necessary, we do 
>> some magical caching, but that'd be a premature optimization at this 
>> point.
>> Here's an example:
>> ogr2ogr -a_srs http://spatialreference.org/epsg/4326/proj4 -t_srs 
>> http://spatialreference.org/user/6/proj4 world_borders.shp 
>> world_borders_google.shp
>> Howard
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