# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Ecef**

**From:**Lu Abel

**Date:**2001 Jul 24, 8:35 PM

1. What are the units of measurement? I think I could grasp 1368950/-4603950/4182550 more easily with a unit of measurement. 2. I don't necessarily agree that it might make determination of our centroid easier. An average in ECEF coordinates would easily give us a point in the middle of the earth! Don't know about you, but I prefer sailing to digging :-) Lu Abel At 10:31 PM 7/24/2001 +0000, you wrote: >Earth Centered Earth Fixed Cartesian coordinates. > >The origin is at the center of the earth. The positive z-axis goes through the >N-pole. The positive x-axis goes through the equator and the Greenwich >meridian. The y-axis completes the orthogonal system. > >Roughly speaking, ECEF coordinates are what you get when you use the formula >given by R. van Gent and multiply with the radius of the Earth in meters. > > x = R * cos(lat) * cos(long) > y = R * cos(lat) * sin(long) > z = R * sin(lat) > >Strictly speaking, you must account for the spheroidal shape of the earth. > >These coordinates are easier to use in computers because all trigonometry >becomes algebra. Your GPS reciever uses them internally, astronomers need them >for exact topocentric reductions, or surveyors, for instance when they have to >transform maps from one datum into another. > >There goes: > >Herbert Prinz (from 1368950/-4603950/4182550 ECEF) > > >Dan Allen wrote: > > > > > Just what are ECEF coordinates? I've never heard of them.