[OSRS-PROJ] Roussilhe Oblique Stereographic

[Clifford J Mugnier]

Roussilhe once was the Hydrographer of the French Navy.  His oblique
stereographic projection is discussed by me in my September 2000 column on
the Grids and Datums of Poland.  (www.ASPRS.org/resources.html) Although
this is a double projection similar to what the late John P. Snyder
presented, John chose not to present the complete direct and inverse
formulae (that he asked for and that I mailed to him in the middle to late
1980s) since it was not a specific math model used by the United States
Geological Survey.

Roussilhe's work is not obscure.  It is published in the open "Annals
Hydrographique" journals of the early 1900s.  However, you DO have to be
able to read French, and you DO have to open the tomes and look for the
stuff.  Much of the original conformal developments on the ellipsoid of
revolution is in French.  It is not obscure unless you don't read French or
you do not care to try.

This same projection is used for many harbor surveys of the French Navy in
African coasts, both western and northern as well as southeastern around
Madagascar and Reunion.  It is kinda rare in the Pacific French colonies.
It was the national projection of Syria for about a century!

This happens to be a specific truncation of the Bulgarian Geodesist,
Hristow's developments published in "Zeitschrift fur Vermessungswessen" in
the 1930s and 1940s.

The EPSG source should only be used in cases of desperation.

Cliff Mugnier
LOUISIANA STATE UNIVERSITY

----------------------------------------------------

Two of Snyder's coauthored books include some information on
this projection for the forward case (geographic->cartesian) but
no information on the inverse.  Each description of the Roussilhe
is sufficiently different to make thing confusing.  Going
to the original article may be difficult for two reasons: language
and obscurity.

Snyder has his own oblique stereographic and EPSG lists another
flavor.  At the moment, libproj4 only supports Snyder's version.

As for latitude of true scale, this is usually only used in the polar
version.  k_0 is more appropriate for oblique and equatorial.

If precision is not a criteria, then I suggest using Snyder's
Stereographic (in all versions of PROJ and probably in GRASS'.
(I use precision in the sense of matching Roussilhe and not in
terms of Snyder's method).

I did find a site that looks Interesting:

http://www.atomnet.pl/~geodeta/2000/59text1.htm

BUT I can't read Polish.

Incidentally, some tables in above list k_0 factors.

On Mar 9, 2004, at 5:36 PM, <werchowyna at pf.pl> wrote:

> Hello everyone! This my first post to this list. My name is Maciek.
>
> I'm using Grass 5.03.
>
> I need to make a mapset in a projection called Roussilhe Oblique
> Stereographic (alias
> Quasi-Stereographic).
>
> The system name is "Uklad 1965" (eng. "System 1965"). It's an old, the
> most
> popular and widely used system in Poland. The ellipsoid is Krassovsky,
> datum
> Pulkovo 1942 modified for Poland.
>
> Issue - there is no projection called like Roussilhe or
> Quasi-Stereographic
> in Grass.
>
> At http://crs.ifag.de they suggest to use Stereographic. Is it right?
> If so,
> then WHAT SHOULD I INPUT FOR "LATITUDE OF TRUE SCALE". No such info is
> provided in any literature regarding the "System 1965".
>
> Any suggestions welcome!
>
> Maciek Sieczka
>
>
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_____________________________________
Jerry and the low riders: Daisy Mae and Joshua

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