[PROJ] Pseudo-mercator

[Martin Desruisseaux]

Hello

Le 01/12/2021 à 23:54, Andrew Patterson a écrit :

> (…snip…) I altered the WKT on that map from Mercator_1SP -> 
> Mercator_2SP and changed 'latitude_of_center' to 'standard_parallel_1' 
> and now it works exactly as in the old GDAL & PROJ.
>
Note: in EPSG database version 7.6 and later:

  * "Mercator (1SP)" has been renamed "Mercator (variant A)"
  * "Mercator (2SP)" has been renamed "Mercator (variant B)"
  * There is also a "Mercator (variant C)"

Maybe the renaming was done for making room for variant C, I don't know. 
As Even said:

  * Variant A has a "Scale factor at natural origin" parameter.
  * Variant B has a "Latitude of 1st standard parallel" parameter.
  * Variant C has a "Latitude of false origin" parameter in addition of
    standard parallel.

The "latitude of center" parameter name in the old WKT may be confusing. 
While variant B seems to work, having "center" in the parameter name 
gives the impression that the projection could be variant C. The 
"Latitude/longitude of false origin" of "Mercator (variant C)" define 
the location where projected coordinates are (0,0), which may look like 
a projection center (by contrast, "Latitude of 1st standard parallel" 
does not have this effect).

     Martin

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