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What's the 1/6 rule, Daan, and how much does it deviate from the
optimal formula? <br>
<br>
BTW Nice Java applet to study projection deformations here:<br>
<br>
<a class="moz-txt-link-freetext" href="http://www.uff.br/mapprojections/Albers_en.html">http://www.uff.br/mapprojections/Albers_en.html</a><br>
<br>
Pity they didn't make it possible to alter projection parameters like
standard parallels.<br>
<br>
Jan <br>
<br>
On 15-2-2010 21:04, strebe wrote:
<blockquote cite="mid:2C1B7FAB.76DF.4D31.AEC0.3B87D1ABB14C@aol.com"
type="cite">
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>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.</div>
<div>
<div><br>
</div>
</div>
<div>Regards,</div>
<div>
<div>— daan Strebe</div>
<div><br>
</div>
<div><br>
</div>
<div>On Feb 15, 2010, at 9:31:45 AM, "Jan Hartmann"
<a class="moz-txt-link-rfc2396E" href="mailto:j.l.h.hartmann@uva.nl"><j.l.h.hartmann@uva.nl></a> wrote:<br>
<blockquote
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width="70px"><span>From:</span></td>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: black; text-align: left; vertical-align: top; padding-left: 5px;"><span
title=""Jan Hartmann" <j.l.h.hartmann@uva.nl>">"Jan Hartmann"
<a class="moz-txt-link-rfc2396E" href="mailto:j.l.h.hartmann@uva.nl"><j.l.h.hartmann@uva.nl></a></span></td>
</tr>
<tr>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: gray; text-align: right; vertical-align: top; font-weight: bold;"
width="70px"><span>Subject:</span></td>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: black; text-align: left; vertical-align: top; padding-left: 5px;"><span
style="font-weight: bold;">Re: [Proj] Standard projection for
Mediterranean basin</span></td>
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<tr>
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width="70px"><span>Date:</span></td>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: black; text-align: left; vertical-align: top; padding-left: 5px;"><span>February
15, 2010 9:31:45 AM PST</span></td>
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<tr>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: gray; text-align: right; vertical-align: top; font-weight: bold;"
width="70px"><span>To:</span></td>
<td
style="font-family: 'Lucida Grande'; font-size: 8pt; color: black; text-align: left; vertical-align: top; padding-left: 5px;"><span
title=""PROJ.4 and general Projections Discussions" <proj@lists.maptools.org>">"PROJ.4
and general Projections Discussions" <a class="moz-txt-link-rfc2396E" href="mailto:proj@lists.maptools.org"><proj@lists.maptools.org></a></span></td>
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<div id="felix-mail-content-block"
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<div>Could you explain the relationship between Authalic Latitude
and Equal Area projections? There is an article by John Snyder at<a
moz-do-not-send="true" class="moz-txt-link-freetext"
href="http://www.jstor.org/stable/2562645?seq=1"
title="http://www.jstor.org/stable/2562645?seq=1">http://www.jstor.org/stable/2562645?seq=1</a>,
but it's a bit above my mathematical head.<br>
<br>
Jan<br>
<br>
On 15-2-2010 18:01, Clifford J Mugnier wrote:
<blockquote
cite="mid:B597ADFC46B67741B18EA6AA13613FF7EC29EF@email002.lsu.edu"
type="cite">
<div id="idOWAReplyText66217" dir="ltr">
<div dir="ltr"><font color="#000000" face="Times New Roman"
size="2">So?</font></div>
<div dir="ltr"> </div>
<div dir="ltr"><font size="2">Keep the parameters and just use
Authalic Latitude.</font></div>
<div dir="ltr"> </div>
<div dir="ltr"><font size="2">Easy.</font></div>
<div dir="ltr"> </div>
</div>
<div id="idSignature82813" dir="ltr">
<div><font color="#000000" face="Times New Roman" size="2"><span
style="font-size: 10pt;">Clifford J. Mugnier, C.P., C.M.S.<br>
Past National Director (2006-2008),<br>
Photogrammetric Applications Division<br>
American Society for Photogrammetry and Remote Sensing<span
class="Apple-converted-space"> </span><br>
and<span class="Apple-converted-space"> </span><br>
Chief of Geodesy,</span></font></div>
<div><font color="#000000" face="Times New Roman" size="2"><span
style="font-size: 10pt;"><span
style="font-size: 10pt; color: black; font-family: 'Times New Roman',serif; font-variant: small-caps;">Center
for GeoInformatics</span></span></font></div>
<div><font color="#000000" face="Times New Roman" size="2"><span
style="font-size: 10pt;"><span
style="font-size: 10pt; color: black; font-family: 'Times New Roman',serif; font-variant: small-caps;"></span>Department
of Civil Engineering<span class="Apple-converted-space"> </span><br>
Patrick F. Taylor Hall 3223A<br>
<strong>LOUISIANA STATE UNIVERSITY</strong><span
class="Apple-converted-space"> </span><br>
Baton Rouge, LA 70803<br>
Voice and Facsimile: (225) 578-8536 [Academic]<span
class="Apple-converted-space"> </span><br>
Voice and Facsimile: (225) 578-8925 [Research]<span
class="Apple-converted-space"> </span><br>
Honorary Life Member of the<span class="Apple-converted-space"> </span><br>
Louisiana Society of Professional Surveyors<span
class="Apple-converted-space"> </span><br>
Member Emeritus of the ASPRS<span class="Apple-converted-space"> </span><br>
Member of the Americas Petroleum Survey Group<br>
======================================================<br>
</span><a moz-do-not-send="true"
href="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"
target="_blank"><span style="font-size: 10pt;">http://www.asprs.org/resources/GRIDS/</span></a><br>
<span style="font-size: 10pt;">======================================================</span></font></div>
</div>
<div dir="ltr"><br>
<hr tabindex="-1"><font face="Tahoma" size="2"><b>From:</b><span
class="Apple-converted-space"> </span><a moz-do-not-send="true"
class="moz-txt-link-abbreviated"
href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a><span
class="Apple-converted-space"> </span>on behalf of Gerald I. Evenden<br>
<b>Sent:</b><span class="Apple-converted-space"> </span>Mon
15-Feb-10 08:30<br>
<b>To:</b><span class="Apple-converted-space"> </span>PROJ.4 and
general Projections Discussions<br>
<b>Subject:</b><span class="Apple-converted-space"> </span>Re:
[Proj] Standard projection for Mediterranean basin<br>
</font><br>
</div>
<div>
<p><font size="2">On Sunday 14 February 2010 11:46:30 pm Clifford
J Mugnier wrote:<br>
> From 1925 to 1946, there was a "British Grid" used by the Allied
Forces in<br>
> the Mediterranean. The British Army (GSGS) established the
"Mediterranean<br>
> Zone" for the secant Lambert Conical Orthomorphic Projection where
the<br>
> central meridian was 29° East of Greenwich, and the latitude of
origin was<br>
> 39° 30' N, the scale factor at origin was 0.99906, the False
Easting was<br>
> 900 km, and the False Northing was 600 km.<br>
><br>
> See my column in PE&RS for December of 2002 on Greece.<br>
><br>
> Clifford J. Mugnier, C.P., C.M.S.<br>
...<br>
<br>
I had the inference that the request was for an equal-area
projection---a mode<br>
that I consider preferable for thematic purposes.<br>
<br>
--<br>
The whole religious complexion of the modern world is due<br>
to the absence from Jerusalem of a lunatic asylum.<br>
-- Havelock Ellis (1859-1939) British psychologist<br>
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