[time-nuts] time-nuts Digest, Vol 130, Issue 27

["Björn Gabrielsson"]

Hi Bob,

You are confusing the readers here.

  1) zero altitude relative the WGS84/GPS ellipsoid are often tens of
meters over or below sea level, depending on your location.

  2) zero altitude relative to a geoid (EGM96 or something else) is very
close to sea level.

Then if you think of the ellipsoid as a second order model of the geoid...
we can start comfusing people again.

--

    Björn

> Hi
>
> The gotcha is that the GPS numbers are related to a geoid model and not to
> sea level.
> You can indeed find points that are “underwater” based on the geoid,
> but quite dry in
> real life (and vice-versa).
>
> Bob
>> On May 19, 2015, at 12:26 PM, Demian Martin <demianm.pds at gmail.com>
>> wrote:
>>
>> I would buy that (Google Maps being off) except that I'm less than 2
>> miles from the SF bay and -5M would have me underwater. That may well
>> happen but not for a few years at least. Also the Arbiter does match
>> Google maps pretty closely. It doesn't really matter a lot, just a
>> curiosity.
>>     Demian
>>
>>> Date: Mon, 18 May 2015 18:12:58 -0400
>>> From: Bob Camp <kb8tq at n1k.org>
>>> To: Discussion of precise time and frequency measurement
>> 	<time-nuts at febo.com>
>>> Subject: Re: [time-nuts] Thunderbolt Height Error
>>> Message-ID: <1AE37B6B-35FD-4C5F-95D6-01316D6C4AE1 at n1k.org>
>>> Content-Type: text/plain; charset=us-ascii
>>
>>> Hi
>>
>>> The simple answer is that Google maps may or may not be correct. There
>>> are a lot
>>> of examples of them being off by 10M or more. That said, my *guess*
>>> would be that the
>>> Thunderbolt is closer to the truth.
>>
>>> Bob
>>
>>> On May 18, 2015, at 2:34 AM, Demian Martin <demianm.pds at gmail.com>
>>> wrote:
>>>
>>> I have 2 GPSDO's. A Thunderbolt and an Arbiter 1083A. The Arbiter is
>>> old but
>>> it works fine (and has a Wenzel 5 MHz streamline oscillator in it). It
>>> has
>>> the 1995 firmware issue, and I could get new firmware for it ($$) but
>>> I'm
>>> not using it as a clock, just a frequency source.
>>>
>>>
>>>
>>> I just moved and have re-setup both. They share an antenna. I got both
>>> to do
>>> a self survey. The Arbiter was really close to what Google maps
>>> indicate is
>>> my location. The Thunderbolt was about the same except it has me
>>> underground. The arbiter has the height as +30M. The Thunderbolt as
>>> -6M.
>>> What setting do I have wrong in the Thunderbolt? Would it affect the
>>> operation as a frequency standard in any way?
>>>
>>>
>>>
>>>
>>>
>>> Demian Martin
>>>
>>> San Leandro, CA 94577
>>
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