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<HTML><HEAD><TITLE>RE: GPS Errors</TITLE>
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<DIV><FONT face=Arial size=2>I also posted my GPS question to Garmin and thought
I would share their response with you. Not a technical response as I
wanted, but at least they confirm it will not work.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV>
<DIV><BR><BR></DIV>
<P><FONT size=2>Thank you for contacting GARMIN International,</FONT> </P>
<P><FONT size=2>The GPS system is not accurate in describing elevation. You will
constantly receive readings of +/- 150 feet given a fixed elevation or location.
A couple of other significant points I should quickly make. If you are comparing
one GPS receiver next to another you may be introducing electronic interference
into one or both of the receivers. This will cause the units in some cases to
not only read much differently but also incorrectly. Also, how a particular
signal reacts to these atmospheric articles of degredation is likely varying
from signal to signal and thus from unit to unit. Only having these GPS units
located next to one another does not ensure that they will read the same lat/lon
and even less likely is the idea they will display the same altitude.
</FONT></P>
<P><FONT size=2>Best regards,</FONT> </P>
<P><FONT size=2>Tom Buchman</FONT> <BR><FONT size=2>Product Support
Specialist</FONT> <BR><FONT size=2>GARMIN International</FONT> <BR><FONT
size=2>1-800-800-1020</FONT> <BR><FONT size=2>www.garmin.com</FONT> <BR><FONT
size=2>Fax: 913-397-0836</FONT> </P>
<P><FONT size=2>If replying to this message, Please include all correspondence.
</FONT></P>
<P><FONT size=2>AOL Users please select all text before clicking reply to ensure
the original text is included in your reply.</FONT> </P><BR><BR><BR>
<P><FONT size=2>-----Original Message-----</FONT> <BR><FONT size=2>From: Bob
Chambers [<A
href="mailto:BlueDolphin@rivnet.net">mailto:BlueDolphin@rivnet.net</A>]</FONT>
<BR><FONT size=2>Sent: Friday, September 13, 2002 6:55 AM</FONT> <BR><FONT
size=2>To: sales@garmin.com</FONT> <BR><FONT size=2>Subject: GPS Errors</FONT>
</P><BR>
<P><FONT size=2>I have two Garmin GPS II Plus units and am quite happy with
them. I use</FONT> <BR><FONT size=2>them on our 42 foot sailboat.
This week, I needed to get the height of our</FONT> <BR><FONT size=2>land above
the river and thought of using my two units getting the</FONT> <BR><FONT
size=2>difference in their readings, one at sea level and one up on the
cliff. It</FONT> <BR><FONT size=2>is my understanding that DGPS compares
the measured location versus a known</FONT> <BR><FONT size=2>location and
broadcasts this error signal so that units so equipped can</FONT> <BR><FONT
size=2>correct to an accurate location. The errors removed are atmospheric
errors</FONT> <BR><FONT size=2>and relatively constant over a large area.
Since I did not have DGPS, I</FONT> <BR><FONT size=2>assumed that the
atmospheric error for both of my units side by side would</FONT> <BR><FONT
size=2>also be constant and that they would both give me the same reading.
If</FONT> <BR><FONT size=2>there was an electronic calculation error in one or
both of the units,</FONT> <BR><FONT size=2>perhaps they would be different but
the difference would remain constant. I</FONT> <BR><FONT size=2>put the
units side by side and was shocked to see that they were not only</FONT>
<BR><FONT size=2>different, sometimes by up to 100 feet in altitude, but that
they both</FONT> <BR><FONT size=2>drifted around in different directions.
Sometimes they were the same and</FONT> <BR><FONT size=2>sometimes a hundred
feet apart.</FONT> </P>
<P><FONT size=2>Could you please explain where my thinking was flawed?</FONT>
</P>
<P><FONT size=2>Thanks</FONT> </P>
<P><FONT size=2>Bob Chambers</FONT> </P></BODY></HTML>