[Proj] International 1924 Authalic Sphere needed for EASE-GridSnow data

OvV_HN ovv at hetnet.nl
Thu Nov 6 11:22:34 EST 2008

----- Original Message ----- 
From: "Hamish" <hamish_b at yahoo.com>
To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
Sent: Thursday, November 06, 2008 2:45 PM
Subject: Re: [Proj] International 1924 Authalic Sphere needed for
EASE-GridSnow data

> Markus Neteler wrote:
>> However, the International 1924 Authalic Sphere seems to be
>> missing from PROJ4.
>> Could this be officially added? Is it as simple as this
>> code change (maybe there is a better name to find)?
> definitely a better name would be needed, as International 1924
> Ellipsoid != International 1924 Authalic Sphere!
> http://www.epsg-registry.org/report.htm?type=selection&entity=urn:ogc:def:ellipsoid:EPSG::7022&entity=urn:ogc:def:ellipsoid:EPSG::7057&reportDetail=short&style=urn:uuid:report-style:default-with-code&style_name=OGP%20Default%20With%20Code&title=

I don't get it - I know, it's in the EPSG database.
But: starting from the International 1924 ellipsoid, I get an authalic
radius of 6371227.7113... m.
Why don't they use that value?
Hm, could be the same reason as why they use the well known integer value of
6370997 m for the authalic radius of the Clarke 1966 ellipsoid instead of
the calculated value of 6370997.2406....

Oscar van Vlijmen

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