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View Full Version : What is the formula to convert Lat, Lon, Height to ECEF?



Jorge P
01-16-2012, 08:29 AM
What is the formula to convert Latitude, Longitude, Height to ECEF (Earth Centered Earth Fixed)? Not looking for any code, just the actual math I need to do to get the ECEF and back.

Thanks
Jorge

dmagnus
01-16-2012, 06:51 PM
Does this help?
http://www.satsleuth.com/GPS_ECEF_Datum_transformation.htm

Jorge P
01-17-2012, 01:12 AM
Not really, I can't read the values of a and b. The image is really blurry and small. Zooming doesn't help much.

N, the prime vertical curvature, is that the angle of curvature of the earth? I have read elsewhere that this is not constant due to earths shifting plates, etc... I need something more accurate. Trying to get within centimeters, not meters.

cessnapilot
01-17-2012, 07:39 AM
Jorge:

Check these

http://mathforum.org/library/drmath/view/51832.html

http://www.gmat.unsw.edu.au/snap/gps/clynch_pdfs/coordcvt.pdf

http://agamenon.tsc.uah.es/Asignaturas/it/rd/apuntes/RxControl_Manual.pdf

"Trying to get within centimeters, not meters." you will need a number format with at least 14-15 digits of accuracy.
The accuracy of the input data you enter into the formulas should have about the same accuracy.

You have to take extra care near the poles, better to say near the axis of Earth at some of the formulas.

You are not interested in codes, but if you want to test yours with a bug free bulletproof one, look OBEX for
WGS84 INS computer.

Cheers,

-Istvan

Jorge P
01-18-2012, 09:30 AM
@cessnapilot
Thanks, the mathforum link explains a bit more of what the constants are, linked to in the second post, that I couldn't read.

Jorge P
01-18-2012, 10:10 AM
One more thing, I have been reading some documents on object avoidance from https://www.space-track.org , can't the same methods be applied to ground objects for avoidance?