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

[bg at lysator.liu.se]

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.

--

   Björn

> 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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>
>
>
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