To tell you how far above ground you are, the GPS has to know where the ground is. For that, it is using a model that is not perfect. That is why John Miles' GPS tells him he should get his scuba gear immediately...
If you google "geoid" you will find more than you wanted to know about it. Didier ------Original Message------ From: Michael Baker Sender: time-nuts-boun...@febo.com To: Time-Nuts ReplyTo: Time-Nuts Subject: [time-nuts] Weird T-Bolt elevation readings... Sent: Jan 14, 2010 2:28 PM 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 -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ------------------------ Sent from my BlackBerry Wireless thingy while I do other things... _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.