BjörnIn the case of the Thunderbolt with the default WGS84 datum the height is calculated with respect to the MSL geoid. If another datum is selected the height is calculated with respect to the ellipsoid.
The attached snapshot from the Thunderbolt book makes this clear.
The MSL goeid doesnt coincide exactly with MSL at every point on the Earth's surface.
Bruce [email protected] wrote:
Hi Bruce,The GPS altitude is calculated with respect to the geoid.No, the GPS calculates altitude wrt the ellipsoid. Then its a conversion with lots of coefficients or a lookup table to add the geoid separation. Altitude wrt to the geoid is the same as Mean Sea level, which is what normal maps etc gived height in. -- BjörnThe geoid surface may have a vertical separation from the actual surface by several meters. This correction varies with location on the Earth's surface. Bruce Michael Baker wrote:Hello, TimeNutters-- While we are on a thread about Trimble T-bolts, perhaps someone might expand on why my T-bolt does not ever come up with altitude readings that are even close. After a long fix, the Lat-Lon coordinates are pretty close, but the altitude is always given as around 2 meters. We are pretty low here in Flori-DUH, but not THAT low. My ground elevation here is 28M ABMSL and my GPS antenna is another 8M above that on top of my fireplace chimney. I have roughly 50 ft of RG-59 cable on the antenna, but altering the cable length value does not seem to have any effect. I get these same very low altitude readings with TBOLTMON and Lady Heather v3 beta. Since I know my altitude well withing one meter, should I enter that manually? What is the procedure for doing that? Suggestions...?? Thanks!! Mike Baker ------------------- _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there._______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there._______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
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