[Proj] Difference in Orthographic projection between Proj4 and Global Mapper

[Noel Zinn (cc)]

Hi Huw,

Given ellipsoidal parameters there are many spherical radii from which to choose.  Wikipedia gives a good summary:

https://en.wikipedia.org/wiki/Earth_radius

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?

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.  

Noel

Noel Zinn, Principal, Hydrometronics LLC
+1-832-539-1472 (office), +1-281-221-0051 (cell)
noel.zinn at hydrometronics.com (email)
http://www.hydrometronics.com (website)


From: Huw James 
Sent: Thursday, July 07, 2016 12:35 PM
To: PROJ.4 and general Projections Discussions 
Subject: Re: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper

Dear Noel,


many thanks, I was waiting for you to respond,


Huw




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