[postgis-tickets] [PostGIS] #2918: Use GeographicLib functions for ST_Azimuth, ST_Distance and ST_Project

[PostGIS]

#2918: Use GeographicLib functions for ST_Azimuth, ST_Distance and ST_Project
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 Reporter:  mwtoews  |       Owner:  pramsey      
     Type:  patch    |      Status:  new          
 Priority:  medium   |   Milestone:  PostGIS 2.2.0
Component:  postgis  |     Version:  trunk        
 Keywords:           |  
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Comment(by karney):

 A couple of comments on this ticket:

 (1) A table of how the error varies as you alter
 GEOGRAPHICLIB_GEODESIC_ORDER is given in table 2 of

     http://arxiv.org/abs/1102.1215

 Unless there's a real permformance hit in a realistic application, I
 recommend sticking with the default order.

 (2) If you want some test areas that GeographicLib can handle OK, but
 many existing area algorithms have problems with, try the following
 triangle on a '''sphere''':
 {{{
     lat lon
     80 0
     0 0
     40 0.00001
 }}}
 This causes problems for some algorithms because they use a formula for
 the area in terms of the lengths of the sides.  For a sphere of radius
 6400 km, the area is 3986457.56957 m^2

 (3) You might want to consider exposing the differential quantities
 associated with geodesics.  Here's the solution of the closest approach
 problem using Newton's method

 https://sourceforge.net/p/geographiclib/discussion/1026620/thread/33ce09e0/

 This uses the reduced length and geodesic scale to compute the derivative
 needed by Newton's method.

-- 
Ticket URL: <http://trac.osgeo.org/postgis/ticket/2918#comment:17>
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