[time-nuts] Weird T-Bolt elevation readings...

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Jan 14 20:57:48 UTC 2010


The GPS altitude is calculated with respect to the geoid.
The 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
> -------------------
>
>
>
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