Craig, > The way I handle it is (slightly older notation): > > PROJCS["WGS84 / Spherical Mercator", > GEOGCS["WGS84basedSpheric_GCS", > DATUM["WGS84basedSpheric_Datum", > SPHEROID["WGS84based_Sphere", 6378137, 0]], > PRIMEM["Greenwich", 0], > UNIT["degree", 0.0174532925199433]], > PROJECTION["Mercator"], > PARAMETER["latitude_of_origin", 0], > PARAMETER["central_meridian", 0], > PARAMETER["false_easting", 0], > PARAMETER["false_northing", 0], > UNIT["meter", 1], > AUTHORITY["EPSG", "3857"]] >
The above WKT using plain Mercator and a sphere definition could potentially result in incorrect datum transformation being done by some systems if transforming coordinates from a non-WGS84 based CRS to this definition (actually just testing it with PROJ >= 6 or GDAL <= 2.4, it rejects its because it doesn't know the 'Mercator' projection method. Should be 'Mercator_1SP' for the WKT1 dialect that GDAL/PROJ speaks) Jukka was quite correct: EPSG:3857 is defined on the WGS 84 datum, but the projection method to use is spherical mercator, that is forcing flattening to 0. See https://epsg.org/crs/wkt/id/3857 > Will GDAL accept a "0" for the inverse of flattening to represent a sphere? Yes. That's the canonical way of expressing a sphere Even -- Spatialys - Geospatial professional services http://www.spatialys.com _______________________________________________ gdal-dev mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/gdal-dev
