[PROJ] Pseudo-mercator

[Andrew Patterson]

Martin,

> 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).
>
That's actually really interesting -- thanks for the additional
information! I'll keep an eye out for those variants.

I also 'misspoke' when I said 'latitude_of_center' -- I believe it's
actually 'latitude_of_origin'. I can see that 'latitude_of_center' is in
the original WKT but I have no idea why. I went back to the original WKT
and it has 'latitude_of_origin'. I know I didn't alter the WKTs, so I'm
very confused about where the 'center' came from. I'm not sure if that
matters or not to your suggestion that this might be variant C or not
though.

..............................
Andrew Patterson
Lead Software Architect
Avenza Systems Inc.

email: andrew at avenza.com
phone: 416.487.5116
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