[ntp:questions] Sure Electronics GPS board: Amazing performance. :-)

unruh unruh at wormhole.physics.ubc.ca
Fri Apr 1 05:58:31 UTC 2011

On 2011-03-31, Chris Albertson <albertson.chris at gmail.com> wrote:
> On Thu, Mar 31, 2011 at 9:44 AM, Uwe Klein
><uwe_klein_habertwedt at t-online.de> wrote:
>> unruh wrote:
>>> My only concern is that the unit places its location 12m away from its
>>> actual location on Googleearth-- ie, either googleearth is 12 m out in
>>> its alignment to lat/long grid at my house, or the unit is misreporting
>>> its position.
> Another possibility to check is that both are not using the same
> system.  What spheroid dose Google use?  Is it WGS84?   The GPS would
> need to be set to match whatever Google uses.  Errors on the order of
> up to 100M are posable.  Not everyone uses the same system.
> Better than Google are the USGS topographic maps.  These are now
> available on-line for free.  These are surveyed maps verified by
> surveyors on the ground.  If you are worried about errors on the order
> of a few meters Google is likely not the best source (except to help
> you find the USGS.)
> I've got it easy because a while back we did some construction at the
> house and the city made us hire a survey team to find the true
> location of the lot lines.  So now I have a surveyed bronze marker
> right on the driveway.

Did they use differential GPS? We have a city survey marker near our
house-- the problem is that they charge to give you the information. 
Did the surveyors tell you what the location of that marker was? 

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