[OSM-talk] [Fwd: Re: [Talk-ca] What's good accuracy for a GPS unit?]

[simon at mungewell.org]

Sorry, meant to send to 'talk' not 'talk-ca'....

Simon

---------------------------- Original Message ----------------------------
Subject: Re: [Talk-ca] [OSM-talk] What's good accuracy for a GPS unit?
From:    simon at mungewell.org
Date:    Tue, April 13, 2010 4:59 pm
To:      "Phil! Gold" <phil_g at pobox.com>
Cc:      "Talk-CA OpenStreetMap" <talk-ca at openstreetmap.org>
--------------------------------------------------------------------------


> What I'm curious about is how well the Pre's accuracy compares to other
> GPS units.  I've read that GPS units with WAAS (for I am in the US) can
> get results with less than one meter of imprecision, but in a survey of
> GPS unit accuracy online I only found reports of "3 meters or less".
>
> What's the typical degree of accuracy you get with your GPS unit?

Generally you would expect to see somewhere around 3m or 4m quoted
accuracy, this is only an estimation as the thing doesn't really know
where it is.

With a _really_ good constellation of satellites (which changes all the
time) you may get slightly better results. The main problem is the
uncertancy/variation of the effects of the atmosphere.

If you want better result you will have to post-process raw data (which
most consumer grade receivers can't output), or use an RTK (Real Time
Kinematic) system which again required raw data and a second 'reference'
GPS receiver.

With RTK and a L1 receiver you can get in the order of 5cm to 2cm, L1+L2
RTK gets below 1cm accuracy.

If you want to 'play' with raw data you could do worse that check out the
open source project 'RTK-Lib':
http://gpspp.sakura.ne.jp/rtklib/rtklib.htm

Cheers,
Simon.



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