[Proj] Distance between pair of lat / lons
Clifford J Mugnier
cjmce at lsu.edu
Wed Dec 26 17:38:18 EST 2012
Legal Applications of Geodesic Formulae - Forensic Geodesy
I do a great deal of consulting work for Attorneys as an Expert Witness, primarily with respect to Photogrammetry. On occasion, I am asked to compute distances for submission in pleas for Summary Judgements.
When I use ellipsoidal geodesics (normally the inverse case), I always use whatever is published by the United States National Geodetic Survey. Irregardless of the accuracy returned (which is quite good for several hundred miles/kilometers); it is what is legally considered as the "National Standard" recognized by our national U.S. government.
Keep that in mind when doing such calculations in your country of residence; supreme accuracy is not as important as legal accuracy.
LOUISIANA STATE UNIVERSITY
From: proj-bounces at lists.maptools.org [proj-bounces at lists.maptools.org] on behalf of Charles Karney [charles.karney at sri.com]
Sent: Wednesday, December 26, 2012 3:16 PM
To: proj at lists.maptools.org
Subject: Re: [Proj] Distance between pair of lat / lons
On 12/25/2012 11:46 AM, Jayesh Chaudhary wrote:
> We have been using GeoographicLib and it had a convenient function to
> calculate distance between two points with an error in the range of nm.
> I am familiar with PROJ4 but I don't see any such function in PROJ4. We
> do care about accuracy and therefore I am not willing to use simple
> methods that consider earth as perfect to compute such distance.
> Please let me know if there is such functionality exists in PROJ4.
The geod program in proj.4 version 4.8.0 is based on the work of Thomas
(1970). The accuracy of this method is limited and the inverse method
fails for nearly antipodal points.
In the next(?) version of proj.4, geod will use the geodesic routines
from GeographicLib which cures the defects in Thomas' method.
I hope that this version will also add the geodesic routines in the
proj.4 library so that you can incorporate geodesic calculations into
any code which links against proj.4.
Charles Karney <charles.karney at sri.com>
SRI International, Princeton, NJ 08543-5300
Tel: +1 609 734 2312
Fax: +1 609 734 2662
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