[Proj] Roussilhe Projection

Clifford J Mugnier cjmce at lsu.edu
Mon Oct 24 11:28:28 EDT 2005

The Roussilhe Stereographic Projection was published in the early 1900s by
the Hydrographer of the French Navy, Roussilhe.  Although his formulae,
adopted by several European Powers, are computationally unique; that has
absolutely NOTHING to do with a datum shift.  The various "block
interpolations" are just variations on the implementation of NADCON or
NTv02 algorithms shifting from one coordinate reference frame to another -
not projections.

Of use? Certainly.  However, I sense that there is some confusion between
the implementation of an analytic function for a map projection and the
implementation of a datum shift.

I recommend that you keep the two concepts separate rather than combining
the topics under the subject of the Roussilhe Stereographic Projection.
(Note there is ALSO the Hristow Stereographic Projection as used in Romania
as the "Stereo 70.")  Roussilhe (Russell), was French; Hristow was
Bulgarian and he published in German.

Clifford J. Mugnier
Chief of Geodesy and
Associate Director,
Department of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-4474 [Research]

> From: "Gerald I. Evenden"
>> And their document about this epmirical corrections, only in Polish:
> I would be very interested in  a translation and would be glad to
> the PASCAL code to C and include in a Polish system variant for libproj4
if it
> represents what is in practical use by the Poles.

Does this mean that there is an intention to incorporate ALL available grid
corrections into the code of libproj4?
The Dutch cadastre provides upon request NLGEO2004 correction data for the
RD, the Australians have National Transformation Grids for AGD66 and AGD84,
the French IGN has several grid corrections available, and undoubtedly
are many more countries with freely or for minimal charge available data
sets and procedures.
All in all this could add 100s of MB to the libproj tarball. Please make
sure you also make a version without grid data available!

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