[aprssig] garmin gps and compass heading

Robert Bruninga bruninga at usna.edu
Sat Apr 29 11:22:29 CDT 2006

I need 3 of these magnetic heading chips for our
next satelltie to build the magnetometer.  ANyone
have any experience with them?  Bob

>>> ramirault at verizon.net 04/28/06 8:54 PM >>>
----- Original Message ----- 
From: "Wes Johnston"
Subject: [aprssig] garmin gps and compass heading

Does anyone know if the garmin units with compasses output a seperate 
compass heading?  Note that the compass heading may be different than the 
direction of travel (for example if the unit is held horizontal and moved 
backwards or left/right.)  My intent is to have a serial compass that shows 
which way the gps unit is oriented.

No idea with those garmins.  You do realize that a 'heading' (towards the 
next waypoint for instance) on the display IS dependant on the orientation 
of the GPS .. at least hand held units (I haven't experimented with any 
hocky puck units).

A GPS expects to be held, face up, with the "top" of the unit towards the 
direction of travel.  For instance if you are in a car, moving forward, and 
the GPS says that the next waypoint is 90 deg to the right.  THEN, if you 
stop and backup the car WITHOUT moving the GPS in any way .. the GPS will 
tell you that the waypoint is now 90 deg to the LEFT!! so long as the car is 
still moving backwards.

What all this has to do with compass output (with those GPS units with an 
electronic compass.. the only ones in consideration here I hope) ??  I have 
no idea.

Richard Amirault                                N1JDU                Boston, 
n1jdu.org                                   "Go Fly A Kite" 

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