[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:         
Component:  postgis  |     Version:  trunk  
 Keywords:           |  
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Comment(by mwtoews):

 Looking at the existing Vincenty methods in PostGIS, it looks like "near
 antipodal" is just under 1 mm distance away from the true antipode for
 ST_Distance to provide reliable numbers, and about 100 m distance for
 ST_Azimuth to provide reliable numbers. So it seems that "near antipode"
 is a corner case.

 More importantly, I'm yet to compare the results between existing
 Vincenty's to Karney's methods. It is claimed that Vincenty's is less
 accurate, but I'd like to quantify this figure. The round-off errors are
 less than 15 nanometers. Also, the benchmarking done in Karney (2013) is
 essentially the same what I've found for the inverse methods (ST_Distance,
 ST_Azimuth): compare 2.34 μs to 1.34 μs for Vincenty's, or just over twice
 as slow. So there were never claims that GeographicLib were faster than
 existing methods. However, for things like ST_Segmentize for straight
 lines, each additional point can be found in 0.37 μs. Section 7 of the
 paper describes the implementation, and is a good and short read that is
 highly relevant for this ticket.

 I'll set-up `ptarray_area_spheroid` to do something similar to
 [http://geographiclib.sourceforge.net/html/C/planimeter_8c_source.html the
 `planimeter.c` example] to get a good idea of the area calculation
 abilities. The error in the area calculation in GeographicLib is about 0.1
 m².

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Ticket URL: <http://trac.osgeo.org/postgis/ticket/2918#comment:7>
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