[NatureNS] GPS deal - spatial resolution

From: Bob McDonald <bobathome@hfx.eastlink.ca>
To: naturens@chebucto.ns.ca
References: <d15.5570b072.380f105c@aol.com>
Date: Thu, 22 Oct 2009 11:50:40 -0300
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Hi All,

Although I have no special knowledge regarding the spatial resolution of GPS receivers, I do have the perspective of a user.  One of my applications is in the game called "geocaching".  Cachers normally use small hand-held units (Garmin is the company which sells most of the small units used by cachers) which sell for $150 to $500.  Units which sell for less than about $200 have a receiver which is less sensitive and so in deep cover may loose the signal.  However they are not necessarily less accurate than the more expensive hand-helds.  Estimated accuracy is at best +/- 5m.  The more expensive units (my Garmin Map 60 Cx cost about $325 at MEC) find the satellite signals much faster, have a much more sensitive receiver (do not loose signal even inside the house) and MAY be more accurate - my unit indicates that the accuracy is +/- 3m, with medium to strong signals from 9 satellites.
If the accuracy were only +/- 10 m, these units would be next to useless for caching.

At the other end of the scale, I understand that surveyors and others who require better than 1m accuracy use back-pack type units with long antennas and they can achieve an accuracy of a few cm at best (I've seen +/- 10cm quoted).  My feeling is that accuracy quoted of a few mm is impossible!

Cheers,

Bob McDonald
Halifax
bobathome@eastlink.ca

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<DIV><FONT size=2>Hi All,</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Although I have no special knowledge regarding the spatial 
resolution of GPS receivers, I do have the perspective of a user.&nbsp; One of 
my applications is in the game called "geocaching".&nbsp; Cachers normally use 
small hand-held units (Garmin is the company which sells most of the small units 
used by cachers) which sell for $150 to $500.&nbsp; Units which sell for less 
than about $200 have a receiver which is less sensitive and so in deep cover may 
loose the signal.&nbsp; However they are not necessarily less accurate than the 
more expensive hand-helds.&nbsp; Estimated accuracy is at best +/- 5m.&nbsp; The 
more expensive units&nbsp;(my Garmin Map 60 Cx cost about $325 at MEC) find the 
satellite signals much faster, have a much more sensitive receiver (do not loose 
signal even inside the house) and MAY be more accurate - my unit indicates that 
the accuracy is +/- 3m, with medium to strong signals from 9 
satellites.</FONT></DIV>
<DIV><FONT size=2>If the accuracy were only +/- 10 m, these units would be next 
to useless for caching.</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>At the other end of the scale, I&nbsp;understand that 
surveyors and others who require better than 1m accuracy use&nbsp;back-pack type 
units with long antennas and they can achieve an accuracy of a few cm at best 
(I've seen +/- 10cm quoted).&nbsp; My feeling is that accuracy quoted of a few 
mm is impossible!</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Cheers,</FONT></DIV>
<DIV><FONT size=2></FONT>&nbsp;</DIV>
<DIV><FONT size=2>Bob McDonald</FONT></DIV>
<DIV><FONT size=2>Halifax</FONT></DIV>
<DIV><FONT size=2><A 
href="mailto:bobathome@eastlink.ca">bobathome@eastlink.ca</A></FONT></DIV></BODY></HTML>

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