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

[Redoute]

Am 16.09.2015 um 20:31 schrieb Andre Joost:

Thank you for your explanations. The discussion if Web Mercator is
conformal or non conformal seems academical to me. And I never
understood why the unit in CRS 3857 is called "meter", it should be
called "unit" to avoid mistakes. The central point however seems to be

> The proj.4 definition is:
> which uses a sphere, while the WKT definition in the .prj file is using 
> the ellipsoid:

Are you saying that it is not possible to fully describe this projection
as WKT without using a "PROJ4 extension" (or to reference auth ids that
use a "PROJ4 extension")?

And this extension is that new/uncommon, so that it cannot be written
into the primary prj file? Meaning that exchanging CRS 3857 shapefiles
between different applications, e. g. from QGIS to CartoDB, will ever
result in heavy projection errors?

Redoute (Kai Borgolte, Bonn)