[gdal-dev] Encoding EPSG:3857 (WebMercator) in GeoTIFF, and ArcGIS interoperability

[Even Rouault]

> 
> The way I see it, there are two different ways to model Google Mercator:
> 1. As a WGS84 datum/ellipsoid with a custom Mercator-based projection
> which uses only the semi-major axis, as seems to be currently done in
> EPSG: http://epsg-registry.org/export.htm?wkt=urn:ogc:def:crs:EPSG::3857
> 2. As the Google spheroid with Mercator 1SP and no transformation when
> going to WGS 84.
> 
> I don't think #1 is currently an option given the list of coordinate
> transformation codes available in the GeoTIFF specification.

Right, there's no such coordinate transformation for GeoTIFF

> 
> For #2, I would think/hope that if you specified the identity
> 7-parameter transformation in the GeoTIFF header, ArcGIS would properly
> reproject the image:

Hum, this will not work I'm afraid. See my response to Dmitry's to see why 
+towgs84=0,0,0,0,0,0,0 is not appropriate.
(Plus the fact that the +towgs84 in geotiff is probably not very widely 
supported.)

> http://trac.osgeo.org/geotiff/ticket/26
> 
> André
> 
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