[Proj] Re: Newbie Polar stereographic question
Gerald I. Evenden
gerald.evenden at verizon.net
Fri Jul 14 10:33:37 EDT 2006
On Friday 14 July 2006 8:12 am, Oscar van Vlijmen wrote:
> > 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.
I an going to make a single comment: worrying about differences in the 1
micron range are pointless. As long as the results compare to .1mm, call it
a match. And even that may be a bit of overkill.
--
Jerry and the low-riders: Daisy Mae and Joshua
"Cogito cogito ergo cogito sum"
Ambrose Bierce, The Devil's Dictionary
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