[time-nuts] Averaging Location for Position Hold
jmfranke
jmfranke at cox.net
Tue Sep 13 21:23:13 UTC 2011
I believe that should read WGS 84 not WPS84.
John WA4WDL
--------------------------------------------------
From: "Chris Albertson" <albertson.chris at gmail.com>
Sent: Tuesday, September 13, 2011 5:03 PM
To: "Discussion of precise time and frequency measurement"
<time-nuts at febo.com>
Subject: Re: [time-nuts] Averaging Location for Position Hold
> 2011/9/13 Miguel Gonçalves <mail at miguelgoncalves.com>:
>> Hi all!
>>
>> I am installing a timing GPS unit over a new location where I already
>> have a
>> NMEA GPS with PPS (let's call it unit A). The NMEA GPS is logging every
>> 16
>> seconds its GPGGA string.
>
> The Oncore UT+ can does it's own site survey automatically. That's
> the best way.
>
> You can only compare the GPS location with Google if both are using
> the same "system". The most common one today is WPS84 but you need to
> check.
>
> The problem is that the Earth is not a Sphere and different systems
> assume non-sphere shapes. Getting this wrongs gives about the size
> error you observed, more or less.
>
> Also, can you really trust Google Earth as an authoritative source?
> I'm not sure. An interesting test would be to go find a USGS
> benchmark or a section marker near you then enter it's location into
> Google. See if Google hits the marker.
> --
>
> Chris Albertson
> Redondo Beach, California
>
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