[Proj] Implementation(s) for Oblique Stereographic

[Kees Krikke]

Gerald,
 
Thanks! This clarifies a lot. I thought that Roussilhe was the same as the
Oblique Stereographic code in EPSG 7.2 because the epsg database v6.8 states
Roussilhe as an alias of Oblique Stereographic .
 
Regards,
 
Kees
 
 

  _____  

From: Gerald I. Evenden [mailto:gerald.evenden at verizon.net] 
Sent: 26 October 2005 22:26
To: kees.krikke at wanadoo.nl; PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Implementation(s) for Oblique Stereographic



On Wednesday 26 October 2005 02:39 pm, Kees Krikke wrote:

> Thanks Oscar,

>

...

> So if a coordinate system use Oblique Stereographic projection (epsg code

> 9809) you need to know if the epsg (Roussilhe) or usgs implementation

> should be used.

The Oblique Stereographic code in EPSG 7.2 IS NOT Roussilhe. The EPSG code
is the Double Projection method using conformal conversion of the ellipsoid
to the sphere and then using the spherical stereographic projection.
Roussilhe is not mentioned in the EPSG 7.2 publication.

Libproj4 provides for three (3) different Oblique Stereographics
projections: "+proj=stere" for the USGS version (Snyder), "+proj=sterea" for
the Double Projection method and "+proj=rouss" based upon Roussilhe's 1922
paper.

The description of the +proj=sterea projection in the libproj4 manual looks
different from the EPSG description because the process is organized so that
the conformal conversion software is also used by the Krovak and Swiss
projections.

The results of a shell script shows lproj's operation on the EPSG example:

Double Projection Stereographic --- libproj4 +proj=sterea

lproj script parameters:

+a=6377397.155 +rf=299.15281 +lat_0=52d9'22.178 +lon_0=5d23'15.5
+k_0=0.9999079+x_0=155000 +y_0=463000

comparison data from EPSG 7.2 : 196105.283 557057.739

lproj forward projection

196105.283 557057.739 from EPSG 7.2 196105.283 557057.739

Forward->Inverse cycle-binary intermediate

6dE 53dN

Thus thread gets a bit confusing at times and I feel that misuse of
nomenclature is causing some of the confusion.

...

-- 

Jerry and the low riders:Daisy May and Joshua

"The being cannot be termed rational or virtuous,

who obeys any authority, but that of reason."

---Mary Wollstonecraft 1792

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