[maemo-users] [maemo-users] Re: how to determine track's length from GPX-file

From: HighEarthOrbit software at highearthorbit.com
Date: Tue Jul 11 15:42:33 EEST 2006
from: http://www.movable-type.co.uk/scripts/LatLong.html

Since the earth is not quite a sphere, there are small errors in using
spherical geometry; the earth is actually roughly ellipsoidal (or more
precisely, oblate spheroidal) with a radius varying between about
6,378km (equatorial) and 6,357km (polar), and local radius of
curvature varying from 6,336km (equatorial meridian) to 6,399km
(polar). This means that errors from assuming spherical geometry might
be up to 0.55% crossing the equator, though generally below 0.3%,
depending on latitude and direction of travel. An accuracy of better
than 3m in 1km is good enough for me, but if you want greater
accuracy, you could refine the result by using the local radius of
curvature, as explained in the US Census Bureau GIS FAQ.

Alternatively, you could use the Vincenty formulation:

> Date: Mon, 10 Jul 2006 20:51:34 +0100
> From: "Armin M. Warda" <armin.warda at googlemail.com>
> Subject: Re: Fwd: [maemo-users] how to determine track's length from
>         GPX-file
> To: maemo-users at maemo.org,
> Message-ID:
>         <11152561094663348731.1957747793.Armin.Warda at GoogleMail.Com>
> Content-Type: text/plain; charset=UTF-8
> Nils wrote:
> > I do not want to start nitpicking here but that solution is rather inaccurate.
> > It might serve as a first rough estimation
> > but it neglects the fact that the earth is not a perfect sphere.
> How (in-)accurate is it? Possible to quantify?
> Up to 5% error would be tolerable for me,
> because I only use it for cycling.
>   regards, Armin.

Andrew Turner
ajturner at highearthorbit.com        42.4266N x 83.4931W
http://highearthorbit.com              Northville, Michigan, USA

More information about the maemo-users mailing list