[OpenLayers-Trac] [OpenLayers] #3426: Accurate treatment of geodesics

OpenLayers trac-20090302 at openlayers.org
Thu Jul 21 17:19:59 EDT 2011

#3426: Accurate treatment of geodesics
 Reporter:  karney     |       Owner:              
     Type:  feature    |      Status:  new         
 Priority:  minor      |   Milestone:  2.12 Release
Component:  Util       |     Version:  2.10        
 Keywords:  Geodesics  |       State:              
 OpenLayers 2.10 provides distVincenty and destinationVincenty which
 compute geodesics using Vincenty's method.  However this method suffers
 from two problems:

 * the distance calculation fails to converge from some pairs of
 * where it converges the error is rather large (about 0.5mm).

 OpenLayers also provides a function getGeodesicArea which is inaptly
 named because

 * it treats only a sphere and not the ellipsoid;[[BR]]
 * the edges of the polygon are not geodesics (or great circles) but rather
 straight lines on a cylindrical equal-area projection;[[BR]]
 * the polygon cannot enclose a pole.

 The attached patch adds distGeodesic, destinationGeodesic, and
 getTrueGeodesicArea which correct the problems noted about.  These use
 the Javascript port of the geodesic functionality in GeographicLib.  For
 a sample of the capabilities, see


 GeographicLib also provides facilities which may be useful to OpenLayers
 in the future (for instance it can simplify finding the intersection of

 GeographicLib using the MIT/X11 license so you are free to incorporate
 it into OpenLayers.

Ticket URL: <http://trac.openlayers.org/ticket/3426>
OpenLayers <http://openlayers.org/>
A free AJAX map viewer

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