Application: gvSIG desktop

Temporal solution:
gvSIG doesn’t include this projection originally. It’s possible to create it manually if we have the WKT string, but it’s not easy. In this case, the OSM plugin will do it for us. Everytime it’s executed it will check if this EPSG exists in the gvSIG database and if it’s not included it will be created as a user projection. At this way we will be able to change the view to this projection for loading the cartography.

#2306 fixes this feature request only partially: EPSG:3857 and EPSG:3785 are available in the latest version of EPSG Registry, however there's a warning message that says "CRS not supported ======". Instead, EPSG:900913 (that is equivalent to the first two codes) is not an official EPSG code and it can be skipped.

When we try to add a WMTS layer, this error always happens:

java.lang.Exception: The projection'Popular_Visualisation_Pseudo_Mercator' is not a proj4 projection.
     org.gvsig.crs.Proj4.exportToProj4(Proj4.java:3170)
     org.gvsig.crs.Crs.getProj4String(Crs.java:706)
     org.gvsig.crs.Crs.getCrsProj(Crs.java:462)
     org.gvsig.crs.Crs.isProjected(Crs.java:577)
     org.gvsig.raster.wmts.io.WMTSDataParametersImpl.isProjected(WMTSDataParametersImpl.java:265)
     org.gvsig.raster.wmts.io.WMTSProvider.getExtentByResolutionLevel(WMTSProvider.java:532)
     org.gvsig.raster.wmts.io.WMTSProvider.getExtent(WMTSProvider.java:465)
     org.gvsig.raster.wmts.io.WMTSProvider.getAffineTransform(WMTSProvider.java:419)
     org.gvsig.raster.tilecache.io.TileProvider.init(TileProvider.java:326)
     org.gvsig.raster.tilecache.io.TileProvider. (TileProvider.java:262)
    [...]

So the projection 'Popular_Visualisation_Pseudo_Mercator' (used by EPSG:3857) is not recognized as a PROJ.4 projection. Furthermore, 'Popular_Visualisation_Pseudo_Mercator' has not an alias (see EPSG:1024), i.e. there's not an equivalent projection in Proj.4, due to its particular definition (it uses a sphere, but it's also associated to an ellipsoid, WGS84). However, it could be parsed as 'Mercator (1SP)' declaring both semiaxis (see http://www.geotoolkit.org/modules/referencing/faq.html#Google), if possible. For instance, GeoServer uses a specific Mercator1SPGoogle class which extends the Mercator projection (https://github.com/geoserver/geoserver/blob/master/src/main/src/main/java/org/geotools/referencing/operation/projection/Mercator1SPGoogle.java).

See also: http://jira.codehaus.org/browse/GEOT-1511
The approach suggested here consists into allow the definition of minor semiaxis (in place of 1/f which is infinite in this case), just like the "User CRS" wizard is able to do. Then EPSG:3857 is like '"WGS 84 / World Mercator" WKT, except that the "semi_major" and "semi_minor" parameters are explicitly defined.'

Hola Antonio,
He intetado dar de alta la proyeccion 'Popular_Visualisation_Pseudo_Mercator' en la libreria de jcrs.
Se me escapan muchas cosas, pero he creado algo :)
No se como probar si lo que he metido hace algo.
Lo subo al SVN y en el siguiente build de jcrs estara.

gvsig-jcrs:r246

Thank you very much, Joaquín. I think we are very close to the solution. If we will be able to manage correctly this weird projection using the latest EPSG Registry, several new functionalities will unlock their true potential (WMTS and OSM layers above all). ;)

int[] valid_method_code = { 1024, 9800, 9801, 9802, 9803, 9804, 9805, 9806, 9807, 9809, 9810, 9811, 9812, 9813, 9814, 9815, 9602, 9659, 9818, 9819, 9820, 9821, 9822, 9823, 9827, 9829 };

1. create a view and set its CRS as EPSG:3857 (not the "User CRS" already available, but the EPSG official one introduced by the update of EPSG Registry, see #2306);
2. if successfully, try to add a WMTS (or a OSM) layer to the view;
3. finally, if successfully again, add a layer defined in EPSG:4326 and verify if it matches with the WMTS (or OSM) one.

• EPSG:3857 (WGS 84 / Pseudo-Mercator) is well recognized now and can be used with the OSM layers at least.
• EPSG:3785 (Popular Visualization CRS / Mercator) is not supported yet (but it should be, even if it's a deprecated code). Although it's recommended to use EPSG:3857 in place of it. Furthermore, in epsg-registry.org is not shown anymore.
• EPSG:900913 (aka Spherical Mercator or Google Projection) is not an official EPSG code, so it can be skipped or defined as "User CRS" starting from EPSG:3857.