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Author Topic: True North vs Magnetic north  (Read 3969 times)

subsailor343

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True North vs Magnetic north
« on: September 20, 2012, 09:17:08 AM »
I have a Garmin Oregon 450. Does it make a difference to UTM coordinates if I use True North instead of Magnetic.  This is in reference to take UTM coor. from a map and entering them into my unit that is set for true north.

Seldom

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Re: True North vs Magnetic north
« Reply #1 on: September 20, 2012, 09:39:01 AM »
UTM coordinates need to reference true north, because magnetic north will wander around a lot depending on where you are.  So my guess is that true north would be the correct setting. 

The real question is whether your 450 references the compass at all or just translates lat/lon into UTM.  Maybe someone more familiar with the hardware and algorithms can answer that one.

leszekp

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Re: True North vs Magnetic north
« Reply #2 on: September 20, 2012, 02:39:06 PM »
UTM coordinates don't necessarily reference true north, they reference "grid north", which can be up to 3 degrees off true north depending on where you are. I.e. if you walk a constant easting but increasing northing, you may not be moving directly towards true north. If you have your Garmin set to "True North", then it will use true north as the reference direction when measuring bearings and setting offsets.

leszekp

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Re: True North vs Magnetic north
« Reply #3 on: September 20, 2012, 02:42:02 PM »
... but to answer your question (sorry about that), no it doesn't make a difference to your UTM coordinates whether you have True or Magnetic North set.