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

[strebe at aol.com]

The typos, yes. Unfortunate. Even more unfortunate is the fictitious integral given for the length of a geodesic. This was repeated by Fenna in A Compendium of Map Projections. Now we’ll never be rid of it.

— daan
Mapthematics LLC


 

 

-----Original Message-----
From: Noel Zinn (cc) <ndzinn at comcast.net>
To: PROJ.4 and general Projections Discussions <proj at lists.maptools.org>
Sent: Thu, Jul 7, 2016 1:24 pm
Subject: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper




Frederick Pearson, II?  I didn't know that, Cliff, but, after going down the rat holes of innumerable typos in his book "Map Projections: Theory and Applications", I sort of gave up on Pearson.  CRC Press didn't serve him well.  -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: Clifford J Mugnier 
Sent: Thursday, July 07, 2016 2:28 PM
To: ndzinn at comcast.net ; vanadovv at hetnet.nl ; PROJ.4 and general Projections Discussions 
Subject: Re: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper

 

Noel,
 
Which then begs the question, why not use the Authalic Latitude function for your spherical equal area projection …
 
That’s what Pearson tried to do when proposed the idea for the old Bonne projection applications in reproducing 19th century graticules.
Not mathematically equivalent, but that’s what he proposed.
 
Cliff 
 


Clifford J. Mugnier, CP,CMS,FASPRS
Chief of Geodesy,
Center for GeoInformatics (C4G)
266 ERAD (Research)
3335 PFT  (Academic)
Dept. of Civil & Environmental Engineering
LOUISIANA STATE UNIVERSITY
Baton Rouge, LA  70803
Research  225-578-4578
Academic   225-578-8536
Cell          225-328-8975

 


 
From: <proj-bounces at lists.maptools.org> on behalf of "vanadovv at hetnet.nl"
Reply-To: "vanadovv at hetnet.nl", "PROJ.4 and general Projections Discussions"
Date: Thursday, July 7, 2016 at 2:22 PM
To: "PROJ.4 and general Projections Discussions"
Subject: Re: [Proj] Difference in Orthographic projection between Proj4 and Global Mapper

 

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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