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<DIV>Hi Huw,</DIV>
<DIV> </DIV>
<DIV>Given ellipsoidal parameters there are many spherical radii from which to
choose. Wikipedia gives a good summary:</DIV>
<DIV> </DIV>
<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>
<DIV> </DIV>
<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?</DIV>
<DIV> </DIV>
<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. </DIV>
<DIV> </DIV>
<DIV>Noel</DIV>
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<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: 'Calibri'; COLOR: #000000">Noel Zinn,
Principal, Hydrometronics LLC<BR>+1-832-539-1472 (office), +1-281-221-0051
(cell)<BR>noel.zinn@hydrometronics.com (email)<BR>http://www.hydrometronics.com
(website)<BR></DIV>
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<DIV style="font-color: black"><B>From:</B> <A title=huwejames@gmail.com
href="mailto:huwejames@gmail.com">Huw James</A> </DIV>
<DIV><B>Sent:</B> Thursday, July 07, 2016 12:35 PM</DIV>
<DIV><B>To:</B> <A title=proj@lists.maptools.org
href="mailto:proj@lists.maptools.org">PROJ.4 and general Projections
Discussions</A> </DIV>
<DIV><B>Subject:</B> Re: [Proj] Difference in Orthographic projection between
Proj4 and Global Mapper</DIV></DIV></DIV>
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<DIV>Dear Noel,<BR><BR></DIV>many thanks, I was waiting for you to
respond,<BR><BR></DIV>Huw<BR>
<DIV class=gmail_extra> </DIV></DIV>
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