[Proj] Optimal Albers Standard parallels

OvV_HN ovv at hetnet.nl
Tue Feb 23 11:43:47 EST 2010

----- Original Message ----- 
From: "strebe" <strebe at aol.com>
To: "PROJ.4 and general Projections Discussions" <proj at lists.maptools.org>
Sent: Sunday, February 21, 2010 8:41 PM
Subject: Re: [Proj] Optimal Albers Standard parallels

> Oscar:

> From the publication you cited
> (http://www.ec-gis.org/sdi/publist/pdfs/annoni-etal2003eur.pdf):

> "A simple but useful way of appraising the location of the origin of an
> azimuthal projection
> is to plot a series of concentric circles of radii z representing the
> isograms of maximum
> Angular Deformation and those of Scale Error at the scale of a convenient
> atlas map
> and to shift this overlay about on the map until a good fit is obtained
> between some
> of the extreme points of the area of mapped."

Like I said, that was my impression indeed.

> ..... I don't know of any non-iterative method for doing that, though
> possibly one could
> be devised. As an algorithmic process, it is not difficult, but unlike
> Albers, it is not just
> a matter of observing the most northerly and most southerly points.

An iterative procedure can always be devised, but I just wondered if there
was (or someone knew of) a closed form.

> I note that you talk about comparing Albers to LAEA.

An interesting point are emotions. Just a hypothesis: try to sell LAEA to an
American client and Albers to a European client. Probably the other way
around works better, whether projection A or B is mathematically better /
more efficient or not.
Such a factor cannot be put into an algorithm!
Are there many examples of US maps in LAEA and Euro maps in Albers?

> Can I interpret your inquiry to mean that you want to know (presumably in
> complete detail)
> the algorithm for finding the projection center of the optimal LAEA for a
> region,...

Nope. Just wondered if you happened to have a quick closed form solution.

Thanks for all the consideration you've given this question so far!

Oscar van Vlijmen

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