[Proj] Re: Newbie Polar stereographic question

Oscar van Vlijmen ovv at hetnet.nl
Fri Jul 14 08:12:42 EDT 2006

> From: "Gerald I. Evenden"

>> I wonder, can all 3 variants of the EPSG (OGP) stereographic projections be
>> calculated with (lib)proj's stere?
> +proj=stere is probably OK for most polar aspects.  However, most non-US
> oblique stereographic projections probably use +proj=sterea.

I am afraid this is no useful answer for
>> EPSG coordinate operation method 9830:
>> Polar Stereographic (variant C)
>> For Projected Coordinate Reference System: Petrels 1972 / Terre Adelie
>> Polar Stereographic

Test case, from the EPSG/OGP guidance note 7.2:
International 1924 ellipsoid
lat=-66d36m8.820s; lon=140d4m17.040s;
latF=-67; lon0=140; x0=3e5; y0=2e5;
Result: x,y = 303169.521856971, 244055.720500674

The ESRI ArcGIS parameters try to 'fool' us with a false northing of
-2299363.487823496 instead of 2e5.
The parameters for (lib)proj stere are then:
International 1924 ellipsoid
lat=-66d36m8.820s; lon=140d4m17.040s;
lat_ts=-67; lon0=140; x0=3e5; y0=-2299363.487823496;
lat0=-90; k0=1;
This gives x,y: 303169.521856971, 244055.720507772

The northing is very close and an even better value of the false northing
would be -2299363.48783059.

I would suggest:

(a) Can someone give an exact formula producing a corrected false easting
for the general case, so that EPSG Polar Stereographic Variant C can be
calculated with (lib)proj.
(b) Or, add EPSG Variant C as an option to (lib)proj stere.
(c) Or simply state 'officially' that EPSG Variant C is not interesting
enough to devote any attention to it.

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