[Proj] Discovery: libproj4 stmerc = French Gauss-Laborde

Oscar van Vlijmen ovv at hetnet.nl
Mon Jun 19 08:09:30 EDT 2006

> From: Strebe-aol.com

> The "trick" is this: Wallis uses the polar stereographic because it's the
> simplest way to get a conformal mapping to the plane. Once the ellipsoid is
> mapped, he treats the plane as the complex plane and looks for a complex
> "co-latitude" which can be used with the polar stereographic, but this time
> treating the polar stereographic as function of a complex variable.

Now where have I seen this again?
Ah yes:

"Transverse Mercator Map Projection of the Spheroid Using Transformation of
the Elliptic Integral software (NPO-18086)."
"... Using the colatitude (complement of latitude) and the longitude
(departure), the initial step is to map the point to the North Polar
Stereographic Projection. The closed-form, analytic function that coincides
with the North Polar Stereographic Projection of the spheroid along the
principal meridian is put into a Newton-Raphson iteration that solves for
the tangent of one half the parametric colatitude, generalized to the
complex plane. ..."

There is documentation available ($) and Fortran software ($). Export out of
the USA is forbidden.
"The program was developed in 1989."

Texts between "" are quotes from web pages found at the Open Channel

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