Web Mercator / Pseudo Mercator¶
New in version 5.1.0.
The Web Mercator / Pseudo Mercator projection is a cylindrical map projection. This is a variant of the regular Mercator projection, except that the computation is done on a sphere, using the semi-major axis of the ellipsoid.
From Wikipedia:
This projection is widely used by the Web Mercator, Google Web Mercator, Spherical Mercator, WGS 84 Web Mercator[1] or WGS 84/Pseudo-Mercator is a variant of the Mercator projection and is the de facto standard for Web mapping applications. […] It is used by virtually all major online map providers […] Its official EPSG identifier is EPSG:3857, although others have been used historically.
Classification |
Cylindrical (non conformant if used with ellipsoid) |
Available forms |
Forward and inverse |
Defined area |
Global |
Alias |
webmerc |
Domain |
2D |
Input type |
Geodetic coordinates |
Output type |
Projected coordinates |
Usage¶
Example:
$ echo 2 49 | proj +proj=webmerc +datum=WGS84
222638.98 6274861.39
Parameters¶
Note
All parameters for the projection are optional, except the ellipsoid definition, which is WGS84 for the typical use case of EPSG:3857. In which case, the other parameters are set to their default 0 value.
- +lon_0=<value>¶
Longitude of projection center.
Defaults to 0.0.
- +x_0=<value>¶
False easting.
Defaults to 0.0.
- +y_0=<value>¶
False northing.
Defaults to 0.0.
Mathematical definition¶
The formulas describing the Mercator projection are all taken from G. Evenden’s libproj manuals [Evenden2005].