[gdal-dev] Add Mercator_variant_A method?

[Even Rouault]

André,

> 
> I am not sure I follow what this has to do with the projection name in
> WKT. The newer WKT specification (ISO 19162) relies solely on the
> identifier to determine which operation method to use to project
> coordinates,

Do you know if there's a publicly available version of ISO 19162 ? I could 
only find this draft on OGC website: 
https://portal.opengeospatial.org/files/?artifact_id=54797 ( accessible from 
http://www.opengeospatial.org/standards/requests/112?utm_source=emailcampaign219&utm_medium=phpList&utm_content=HTMLemail&utm_campaign=The+OGC+requests+comment+on+the+candidate+standard+Geographic+Information+%E2%80%93+Well+Known+Text+for+coordinate+reference+systems 
)

> but the older WKT tends to follow OGC 01-009 which lists
> explicit names to use for the projections. So regardless of what the
> EPSG registry uses for a name, this is the name that is supposed to be
> used for the OGC WKT as far as I am concerned:
> OGC 01-009 (http://www.opengeospatial.org/standards/ct): "Mercator_1SP"

AFAICS, OGC 01-009 is very light on details unfortunatelly (doesn't mention  
parameters of all projections), and things have more or less crystalized by 
the practice of the various vendors (including GDAL/libgeotiff/proj.4). But 
yes, it does mention "Mercator_1SP", and the geopackage spec mentions OGC 
01-009 as the standard to use for WKT.

> 
> I would ask if this is not a bug in the geopackage itself or whatever
> created that WKT string. 

Not geopackage itself, but the NGA's profile on it. But your point on not 
mixing the old OGC 01-009 with ISO 19162 new practice is good, and should 
likely be submitted back to NGA.

> I'm not opposed to mapping that "Mercator variant A" name to
> SRS_PT_MERCATOR_1SP on WKT import, but I think there's a limit to how
> far one should go to support non-standard WKT.

In an ideal world, everyone would follow standards, and there would not be 
many standards/formats to do the same thing ;-) As this world doesn't exist, 
GDAL is there to fill in the gaps. I'd say that it is OK to have some ad-hoc 
rules to accomodate for data found in the wild (but I'm not sure there has 
been data released with the NGA's profile yet ?)

> even spatialreference.org
> is still using "Mercator_1SP" for the OGC WKT.

spatialreference.org is not really maintained AFAIK, and is partly based on an 
old GDAL version. So I wouldn't consider it as an authoritative source.

Even

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