Difference in Orthographic projection between Proj4 and Global Mapper

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Difference in Orthographic projection between Proj4 and Global Mapper

Noel Zinn (cc)
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)
[hidden email] (email)
http://www.hydrometronics.com (website)
 
Sent: Thursday, July 07, 2016 2:28 PM
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: <[hidden email]> on behalf of "[hidden email]"
Reply-To: "[hidden email]", "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 : [hidden email]
Datum : 07/07/2016 19:59
Aan : [hidden email]
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:
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)
[hidden email] (email)
http://www.hydrometronics.com (website)



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Re: Difference in Orthographic projection between Proj4 and Global Mapper

strebe
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) <[hidden email]>
To: PROJ.4 and general Projections Discussions <[hidden email]>
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)
[hidden email] (email)
http://www.hydrometronics.com (website)
 
Sent: Thursday, July 07, 2016 2:28 PM
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: <[hidden email]> on behalf of "[hidden email]"
Reply-To: "[hidden email]", "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 : [hidden email]
Datum : 07/07/2016 19:59
Aan : [hidden email]
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:
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)
[hidden email] (email)
http://www.hydrometronics.com (website)


_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj

_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj