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

Terje Mathisen "terje.mathisen at tmsw.no" at ntp.org
Fri Apr 1 05:51:24 UTC 2011

Chris Albertson 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.

GoogleEarth has many, many tiles of images with far worse registration 
errors than just 3 or 12 m!

In fact, when I zoom in here in Norway and the road layer ends up on top 
of the visible roads I'm very pleased.

> 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.

- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"

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