WGS 84 ellipsoid semi-major (equatorial) axis: 6 378 137.0 m
semi-minor (polar) axis: 6 356 752.3142 m
(biaxial ellipsoid or just ellipsoid is the preferred (at least in North
America) term for spheroid)
What kind of differences might you see when comparing great circle routes on
an approximating sphere with geodesics on the ellipsoid? As an example, the
distance between Washington and L.A. on the sphere is approximately 3711 km.
On the ellipsoid, it is 3719 km.
Here are the expressions for computing the distance in km for one degree of
latitude or longitude on the WGS 84 ellipsoid as a function of latitude, phi:
lat = 111.13295 - 0.55982Cos 2 phi + 0.00117Cos 4 phi
long = 111.41288 Cos phi - 0.09350 Cos 3 phi + 0.00012 Cos 5 phi
See "Navigation 101: Basic Navigation with a GPS Receiver"
<http://gauss.gge.unb.ca/papers.pdf/gpsworld.october00.pdf> for further
details.
"Navigate" is a handy application for computing geodesics on various
ellipsoids for PDAs using the Palm OS:
<http://fermi.jhuapl.edu/navigate/index.html>
-- Richard Langley
Professor of Geodesy and Precision Navigation
On Tue, 3 Feb 2004, Thaddeus Weakley wrote:
>Hello All -
>
>Tony's posting reminds me of a question that I have had for a long time. As
>many of us know, we call geometrically compute the distance between two
>locations (lat, long) and (lat2, long2) assuming that the Earth is a perfect
>sphere (which of course it isn't). Has anyone seen a correction for this
>flattening at the poles, or bowing around the equator? If so, please share.
>
>Thanks,
>
>Thad Weakley
>42.2N, 83.8W
>
>
>
>
>---------------------------------
>Do you Yahoo!?
>Yahoo! SiteBuilder - Free web site building tool. Try it!
===============================================================================
Richard B. Langley E-mail: [EMAIL PROTECTED]
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
===============================================================================
-
