[Proj] ESRI's standard_parallel_1 for Mercator morphedto latitude_of_origin

[Mikael Rittri]

Hello Melita!

Oh, and I already disliked EPSG's variant C for Polar Stereographic. 
I hadn't noticed that there is now a variant C for Mercator, too. 

I agree that they will cause confusion. It is true that they
simplify the few CRS instances where they are used, but
these can be emulated by adjusting the FalseNorthing for
a variant A or B instance instead. And the mere existence of a 
variant C option probably confuses people who don't need it.

> Esri currently supports variant B and the Spherical version

In other words, an ESRI Mercator cannot have a scale_factor?
That means that the ESRI WKT at 

       http://spatialreference.org/ref/epsg/3001/esriwkt/

is wrong.
The result of calling 

       gdalsrsinfo -p -o wkt_esri "epsg:3001"

is also wrong, but in a different way (the scale_factor of 0.997 is replaced
by a standard_parallel_1 as it should be, but the standard parallel value
is 0.0 instead of 4.45405154589751).
      I know Frank et al. have put a great effort into ESRI WKT morphing,
but the task is clearly gigantic.

      So, what's that status of the ESRI branch of GDAL that I've heard 
about? I assume it is a branch of GDAL that is distributed with ESRI
software. Are there any plans to merge the ESRI morphing of this
branch into the GDAL trunk?  

(And top-posting makes journalistic sense: new stuff first.)

Regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com
________________________________________
From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org] on behalf of Melita Kennedy [mkennedy2 at earthlink.net]
Sent: Wednesday, October 17, 2012 7:58 PM
To: proj at lists.maptools.org
Subject: Re: [Proj] ESRI's standard_parallel_1 for Mercator     morphedto latitude_of_origin

(yes, I know I'm top-posting and that it's not customary for the mailing list)

This may only get more confusing with the new EPSG Mercator and Stereographic variants. Currently, there are 4 Mercator variants (ignoring false easting/northing and easting/northing at false origin):

Mercator (Spherical)

  Latitude of natural origin
  Longitude of natural origin

Mercator (variant A) aka 1SP

  Latitude of natural origin (must equal zero)
  Longitude of natural origin
  Scale factor at natural origin

Mercator (variant B)

  Latitude of 1st standard parallel
  Longitude of natural origin

Mercator (variant C)

  Latitude of 1st standard parallel
  Longitude of natural origin
  Latitude of false origin

Esri currently supports variant B and the Spherical version indirectly through Mercator (Auxiliary Sphere) or by using a sphere-based geographic CRS. Esri wants "Central Meridian" and "Standard Parallel 1". Internally, we use an array to store parameters. SP1 and LatOfOrigin use different slots so it wouldn't work by chance either.

Melita


>-----Original Message-----
>From: proj-bounces at lists.maptools.org
>[mailto:proj-bounces at lists.maptools.org] On Behalf Of Mikael Rittri
>Sent: Friday, October 12, 2012 2:33 PM
>To: PROJ.4 and general Projections Discussions
>Subject: Re: [Proj] ESRI's standard_parallel_1 for Mercator morphedto
>latitude_of_origin?
>
[-- text deleted, see http://lists.maptools.org/pipermail/proj/2012-October/006431.html --]