[Proj] FW: SCAR Antarctic PS projection issue in proj

[Oscar van Vlijmen]

>>> -----Original Message-----
>>> From: Mark Fahnestock
....
>>> Here is the detail on the issue I talked to you about regarding
>>> setting up a WCS for the SCAR projection - this projection has an
>>> EPSG identifier, but is not making it in to proj:
....
>>> # WGS 84 / Antarctic Polar Stereographic
>>> # Unable to translate coordinate system into PROJ.4 format.
>>> #
>>> # WGS 84 / Australian Antarctic Polar Stereographic
>>> # Unable to translate coordinate system into PROJ.4 format.

> From: Martin Vermeer <martin.vermeer-hut.fi>
> Googling I found the following old (2002) message by Frank Warmerdam:
> "Generally this happens when there is more than one approximation available
> for
> a datum (to WGS84) in the EPSG tables, as the auto-translation code can't
> decide which to use.  I also doubt that the EPSG to PROJ.4 stuff properly
> accounts for non-greenwich prime meridians.

Let's see how this theory relates to the actual data in the EPSG database.
I used the SQL version 6.7. There is a version 6.8, but at the moment
epsg.org is not connected.
What has the EPSG database to say about: WGS 84 / Antarctic Polar
Stereographic?
(Some not so relevant info not copied here):

>From the coordinate reference system table:

coord_ref_sys_code: 3031
coord_ref_sys_name: WGS 84 / Antarctic Polar Stereographic
area_of_use_code: 1031
coord_ref_sys_kind: projected
coord_sys_code: 4490
datum_code: Null
source_geogcrs_code: 4326
projection_conv_code: 19992
crs_scope: Antarctic Digital Database and small scale (<1:1,000,000) studies
and topographic mapping.

Following the coord_sys_code entry:

coord_sys_code: 4490
coord_sys_name: Cartesian 2D CS for APS. Axes: E,N. Orientations: E along 90
deg East, N along 0 deg meridians. UoM: m.
coord_sys_type: Cartesian
dimension: 2
remarks: Used for South Pole tangential and secant projections.

It's a derived CRS, namely from the CRS mentioned in the field
source_geogcrs_code.
This brings us after a couple of related tables to the basis, which is not
very interesting.
Let's see what the primary coordinate operation is, mentioned in the
original field projection_conv_code.

coord_op_code: 19992
coord_op_name: Antarctic Polar Stereographic
coord_op_type: conversion
source_crs_code: Null
target_crs_code: Null
coord_tfm_version: 
coord_op_variant: Null
area_of_use_code: 1031
coord_op_scope: 1: Antarctic Digital Database and small scale (<1:1,000,000)
studies and topographic mapping. 2: Medium scale studies and topographic
mapping south of 80 deg S.
coord_op_accuracy: 0
coord_op_method_code: 9829
remarks: Special studies may use a different projection using an alternative
longitude of origin. See for example projection code 19993.

The coordinate operation method is:

coord_op_method_code: 9829
coord_op_method_name: Polar Stereographic (variant B)
reverse_op: 1
formula: (see EPSG guidance note #7.2)
example: (see EPSG guidance note #7.2)

The projection parameters can be found in the table
"coordoperationparamvalue" under coord_op_code: 19992
This gives:

False easting: 0
False northing: 0
Latitude of standard parallel: -71
Longitude of origin: 0


In conclusion, my theory is that the projection method is unambiguously
clear, but that either "Polar Stereographic (variant B)" is not supported by
PROJ.4 or that it was somehow not possible to construct relevant PROJ.4
arguments for any PROJ.4 method (stere perhaps) on the fly.