Im trying to define the srs EPSG 3857 inside Terrasolid sofware. I ran into a problem because the definition of the reference ellipsoid is given with a major axis and inverse flatening, not via both axis. Since flatening of a sphere is 0, inverse of a zero is infinite and i cant input that. Doesnt work with a 0, 1 or some very high value either. Any thoughts on how to define it, and if its even possible? The issue is, a sphere (reference body for EPSG 3857) is a kind of ellipsoid that has no flattening, hence you cannot define 1/flatening. Im looking for a workaround in this particular software, or just a confirmation that its in fact impossible to do at this point, since i cannot define datum that involves a sphere as a reference body. First: I can't understand why, if Leaflet uses CRS EPSG:3857, whose unit is meters, I still have to provide coordinates, like maxBounds and center, in WGS84 format, which uses degrees. Is it an API inconsistency? Projections in data are different than display projections. The input to Leaflet is lat/lon in WGS84, the default output is mercator, in EPSG:3857. EPSG:3857 is rarely used for data encodings. I made a double check with a simple wms layer in OpenLayers and a GeoJSON overlay and it works fine, so I proved that the distortion is not in the data. Your OpenLayers map has EPSG:4326 as its display projection, while your Leaflet map has EPSG:3857: this is why one is a different shape. Source.