[time-nuts] Averaging Location for Position Hold

[Chris Albertson]

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