[Qgis-user] What's wrong with PRJ file for CRS 3857?

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Am 17.09.2015 um 05:54 schrieb Andre Joost:

Meanwhile I did some research, this is what I understand:

> No, both WKT definition and proj.4 definition are not capable of 
> defining the transition from ellipsoid to spheroid in the way Google 
> uses it.

Proj4 can: "+nadgrids=@null" is hackish, but I think it does the right
thing using a current Proj4. This is what makes the WKT with Proj4
extension working.

WKT without Proj4-String also can, but you have to give an applicable
PROJECTION parameter, and the software has to implement it. From what I
found on the net, ESRI named their method "Mercator_Auxiliary_Sphere".
GDAL seems to provide no matching method, but not sure about this.

epsg-registry.org now provides WKT strings following the current WKT
standard <http://docs.opengeospatial.org/is/12-063r5/12-063r5.html>. It
uses 'CONVERSION["Popular Visualisation Pseudo-Mercator",
METHOD["Popular Visualisation Pseudo Mercator",ID["EPSG",1024]]'. This
form of WKT is a very recent standard, I don't know which software
currently has support for it. "Operation Method" EPSG 1024 is a textual
description with formulas, how the conversion has to be done. It can be
implemented independent of WKT version.

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