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

vanadovv at hetnet.nl vanadovv at hetnet.nl
Thu Jul 7 12:22:06 PDT 2016


The radius of 6370997 is the integer part of the authalic radius of the Clarke 1866 ellipsoid.
The calculated value would be around 6370997.24063266 m.
Greetings,
Oscar van Vlijmen
 ----Origineel Bericht----
Van : ndzinn at comcast.net
Datum : 07/07/2016 19:59
Aan : proj at lists.maptools.org
Onderwerp : Re: [Proj] Difference in Orthographic projection between Proj4 and	Global Mapper
 
  
   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)
   
  
 
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