[Proj] Standard projection for Mediterranean basin

Jan Hartmann j.l.h.hartmann at uva.nl
Mon Feb 15 13:05:19 PST 2010


What's the 1/6 rule, Daan, and how much does it deviate from the optimal 
formula?

BTW Nice Java applet to study projection deformations here:

http://www.uff.br/mapprojections/Albers_en.html

Pity they didn't make it possible to alter projection parameters like 
standard parallels.

Jan

On 15-2-2010 21:04, strebe wrote:
>
> 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/
>>     <https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/%20%20exchweb/bin/redir.asp?URL=https://email.lsu.edu/%20exchweb/bin/redir.asp?URL=https://email.l>
>>     ======================================================
>>
>>     ------------------------------------------------------------------------
>>     *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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