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[aprssig] Dumb tracker question

Richard Amirault ramirault at verizon.net
Sun Oct 1 03:19:22 UTC 2006


No, it has nothing to do with an internal magnetic compass.  It has to do 
with a GPS assuming that if it is traveling then it is traveling with the 
"top" towards the direction of travel (and face up) so that the arrow 
displayed on the screen is pointing  toward the desired waypoint.

You would not, normally, hold a GPS in your hand with the display facing the 
ground. You would not, normally, hold a GPS in your hand with the "top" 
towards your stomach ("upside down")

If you setup a waypoint and the arrown screen and start moving forward the 
GPS will indicate, using the arrow and a degree listing, a direction toward 
the waypoint.  If you stop and then do nothing but walk (or drive) 
backwards, still facing the same direction as before, the arrow will switch 
direction 180 degrees.

I've only seen this with GPS units that are handheld units, not 'hockey 
puck' types. And it may not happen using a handheld with an external 
antenna.

Richard Amirault                                N1JDU                Boston, 
MA, USA
n1jdu.org                                   "Go Fly A Kite"
----- Original Message ----- 
From: "Wes Johnston, AI4PX" <wes at kd4rdb.com>
To: "TAPR APRS Mailing List" <aprssig at lists.tapr.org>
Sent: Saturday, September 30, 2006 10:39 PM
Subject: Re: [aprssig] Dumb tracker question


> You are correct.... I'd forgotten that some GPS units contain an internal
> magnetic compass.  Usually there is a setting that is adjustable that 
> allows
> the compass to work when the speed is below XX mph.
>
> Wes
>
>
> On 9/30/06, Richard Amirault <ramirault at verizon.net> wrote:
>>
>> ----- Original Message -----
>> From: "Wes Johnston, AI4PX"
>> Subject: Re: [aprssig] Dumb tracker question
>>
>>
>> > If the heading is 180 degrees wrong, maybe turning the GPS antenna on
>> the
>> > car so that the cords comes out near the rear of car will help and
>> correct
>> > the heading?  lol.... couldn't resist!!!
>> (snip)
>>
>> Not as far fetched as you might think.  Many handheld GPS units will give
>> BEARINGS to waypoints that are 180 deg off if they are not held properly
>> ..
>> that is face up with the "top" of the unit towards the direction of
>> travel.
>> For instance if you set the GPS screen to show you an ARROW that points
>> toward the waypoint (that tell you the direction you need to travel to
>> reach
>> that waypoint)  if you reverse the orientations of the GPS in your hand
>> (put
>> the "top" of the unit facing you instead of facing the direction of
>> travel)
>> the arrow will point 180 degrees in exactly the opposit direction you 
>> need
>> to go.  Similarily, if you leave the orientation of the GPS alone and 
>> just
>> walk backwards .. or, if in a vehicle, drive backwards, the same thing
>> will
>> happen.
>>
>> I discovered this when I was an active Geocacher some time ago.
>>
>> Richard
>> Amirault                                N1JDU                Boston,
>> MA, USA
>> n1jdu.org                                   "Go Fly A Kite"
>>
>>
>> _______________________________________________
>> aprssig mailing list
>> aprssig at lists.tapr.org
>> https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig
>>
>>
>


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