[OpenLayers-Dev] projection through urn syntax

[Richard didier]

Le Lundi 4 Mai 2009 14:02, bartvde at osgis.nl a écrit :
> The only question left is do we want to depend on proj4js for this?
>
> Reading urn type projections will require proj4js, is that an acceptable
> dependency for OpenLayers?

If we look at the WMS 1.3.0 specs (for instance), the CRS can be URI 
(EPSG:4326), URN (urn:ogc:def:crs:EPSG:6.6:4326) or URL 
(http://epsg.org/#4326). The process of reading a projection attribute in OL 
is to convert the string definition into an OL.Projection object.

If OL relies upon PROJ4JS, it sounds ok to let PROJ4JS parses the string. 
Either the reader knows and it is ok, or the reader does know and the error 
is handed over back to OL.Projection constructor.

If OL parses the string, it will have to know which one is supported by the 
underlaying reader. The later can evolve and support more and then 
OL.Projection will have to be changed.

So, I prefer the CRS reader understanding or not the string definition and 
OL.Projection just acting as a proxy.

Sincerely,

didier

>
> Best regards,
> Bart
>
> > Hi Didier,
> >
> > great! I had not seen that.
> >
> > So I can just pass a urn string to the OpenLayers.Projection object
> > constructor.
> >
> > Best regards,
> > Bart
> >
> >> Le Lundi 4 Mai 2009 13:25, bartvde at osgis.nl a écrit :
> >>> Hi list,
> >>>
> >>> Currently Proj4js and OpenLayers use EPSG:XXXX as the syntax for
> >>> projections, whereas OWSContext uses the urn syntax, for example:
> >>>
> >>> urn:ogc:def:crs:EPSG:6.6:4326
> >>>
> >>> So in my OWSContext Format I use a small utility function which
> >>> transforms
> >>> this into EPSG:4326.
> >>>
> >>> The urn syntax can also be present in GML3 files.
> >>>
> >>> Question:
> >>> -would this belong in OpenLayers' Projection.js or in Proj4js?
> >>
> >> I have added URN in Proj4js. At least, it is in the trunk (See
> >> http://trac.osgeo.org/proj4js/ticket/17)
> >>
> >> didier
> >>
> >>> Best regards,
> >>> Bart
> >>>
> >>> _______________________________________________
> >>> Dev mailing list
> >>> Dev at openlayers.org
> >>> http://openlayers.org/mailman/listinfo/dev
> >>
> >> --
> >> Didier RICHARD, chef du pôle technique Géoportail pour l'IGN
> >> Institut Geographique National           tel: +33/0 1.43.98.83.23
> >> 2/4 Avenue Pasteur                       fax: +33/0 1.43.98.80.88
> >> F-94165 St-Mande Cedex                e-mail: Didier.Richard at ign.fr

-- 
Didier RICHARD, chef du pôle technique Géoportail pour l'IGN
Institut Geographique National           tel: +33/0 1.43.98.83.23
2/4 Avenue Pasteur                       fax: +33/0 1.43.98.80.88
F-94165 St-Mande Cedex                e-mail: Didier.Richard at ign.fr