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<div>Noel,</div>
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<div>Which then begs the question, why not use the Authalic Latitude function for your spherical equal area projection …</div>
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<div>That’s what Pearson tried to do when proposed the idea for the old Bonne projection applications in reproducing 19th century graticules.</div>
<div>Not mathematically equivalent, but that’s what he proposed.</div>
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<div>Cliff </div>
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<span style="font-weight:bold">From: </span><<a href="mailto:proj-bounces@lists.maptools.org">proj-bounces@lists.maptools.org</a>> on behalf of "<a href="mailto:vanadovv@hetnet.nl">vanadovv@hetnet.nl</a>"<br>
<span style="font-weight:bold">Reply-To: </span>"<a href="mailto:vanadovv@hetnet.nl">vanadovv@hetnet.nl</a>", "PROJ.4 and general Projections Discussions"<br>
<span style="font-weight:bold">Date: </span>Thursday, July 7, 2016 at 2:22 PM<br>
<span style="font-weight:bold">To: </span>"PROJ.4 and general Projections Discussions"<br>
<span style="font-weight:bold">Subject: </span>Re: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper<br>
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<div>The radius of 6370997 is the integer part of the authalic radius of the Clarke 1866 ellipsoid.</div>
<div>The calculated value would be around 6370997.24063266 m.</div>
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<div>Greetings,</div>
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<div>Oscar van Vlijmen</div>
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<blockquote style="margin-right: 0px; margin-left: 15px;">----Origineel Bericht----<br>
Van : <a href="mailto:ndzinn@comcast.net">ndzinn@comcast.net</a><br>
Datum : 07/07/2016 19:59<br>
Aan : <a href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</a><br>
Onderwerp : Re: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper<br>
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<div>Hi Huw, </div>
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<div>Given ellipsoidal parameters there are many spherical radii from which to choose. Wikipedia gives a good summary:
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<div><a title="https://en.wikipedia.org/wiki/Earth_radius" href="https://en.wikipedia.org/wiki/Earth_radius">https://en.wikipedia.org/wiki/Earth_radius</a></div>
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<div>But where does GCTP’s 6370997 come from? It’s close to some radii for WGS84, but no cigar. Is it just a convention? Anyone know?
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<div>Of course, if you’re mapping on a sphere “closeness” shouldn’t really matter very much. Consistency should matter more, and, in that sense, a conventional radius would be useful.
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<div>Noel </div>
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<div style="color: rgb(0, 0, 0); font-family: Calibri; font-size: 12pt;">Noel Zinn, Principal, Hydrometronics LLC
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+1-832-539-1472 (office), +1-281-221-0051 (cell) <br>
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