# [Proj] Standard projection for Mediterranean basin

strebe strebe at aol.com
Mon Feb 15 15:04:24 EST 2010

```I do not understand Dr. Mugnier's response. Using the authalic latitude does not yield an equal-area projection if you project using a conformal projection. I cannot think of any use for mixing authalic latitude with conformal projection.

The purpose of the authalic latitude is to provide an equal-area projection of the ellipsoid onto the sphere. From there you may project to the plane using any spherical equal-area projection, yielding an equal-area projection of the ellipsoid onto the plane. While this technique will not preserve other properties of the spherical projection (such as standard parallels or constant scale along some meridian or somesuch), at least it drastically increases the available projections for ellipsoidal use.

I have, by the way, formulæ somewhere that I derived for computing the optimal standard parallels for Albers given the north/south extents of the map. I will post them if I happen to find them. The 1/6th rule would be fine for any real use, of course. The optimal is more of academic interest.

Regards,
— daan Strebe

On Feb 15, 2010, at 9:31:45 AM, "Jan Hartmann" <j.l.h.hartmann at uva.nl> wrote:
From:   "Jan Hartmann" <j.l.h.hartmann at uva.nl>
Subject:    Re: [Proj] Standard projection for Mediterranean basin
Date:   February 15, 2010 9:31:45 AM PST
To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
Could you explain the relationship between Authalic Latitude and Equal Area projections? There is an article by John Snyder athttp://www.jstor.org/stable/2562645?seq=1, but it's a bit above my mathematical head.

Jan

On 15-2-2010 18:01, Clifford J Mugnier wrote:
So?

Keep the parameters and just use Authalic Latitude.

Easy.

Clifford J. Mugnier, C.P., C.M.S.
Past National Director (2006-2008),
Photogrammetric Applications Division
American Society for Photogrammetry and Remote Sensing
and
Chief of Geodesy,
Center for GeoInformatics
Department of Civil Engineering
Patrick F. Taylor Hall 3223A
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Voice and Facsimile:  (225) 578-8536 [Academic]
Voice and Facsimile:  (225) 578-8925 [Research]
Honorary Life Member of the
Louisiana Society of Professional Surveyors
Member Emeritus of the ASPRS
Member of the Americas Petroleum Survey Group
======================================================
http://www.asprs.org/resources/GRIDS/
======================================================

From: proj-bounces at lists.maptools.org on behalf of Gerald I. Evenden
Sent: Mon 15-Feb-10 08:30
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Standard projection for Mediterranean basin

On Sunday 14 February 2010 11:46:30 pm Clifford J Mugnier wrote:
> From 1925 to 1946, there was a "British Grid" used by the Allied Forces in
> the Mediterranean.  The British Army (GSGS) established the "Mediterranean
> Zone" for the secant Lambert Conical Orthomorphic Projection where the
> central meridian was 29° East of Greenwich, and the latitude of origin was
> 39° 30' N, the scale factor at origin was 0.99906, the False Easting was
> 900 km, and the False Northing was 600 km.
>
> See my column in PE&RS for December of 2002 on Greece.
>
> Clifford J. Mugnier, C.P., C.M.S.
...

I had the inference that the request was for an equal-area projection---a mode
that I consider preferable for thematic purposes.

--
The whole religious complexion of the modern world is due
to the absence from Jerusalem of a lunatic asylum.
-- Havelock Ellis (1859-1939) British psychologist
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