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Magnetic Declination - Yes or No with GPS

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PLC92084
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Magnetic Declination - Yes or No with GPS

Postby PLC92084 » Feb 01 2010 1:36 pm

Laughably, I'm just making the transition from paper maps to GPS. While I can find my way around with either fairly well, I'm wondering what the policy is for setting magnetic declination on a Garmin (or other brand) GPS. I've always adjusted my compass for the map(s) I'm using. Since I haven't had a chance to compare results between paper and digital, does anyone have recommendations for enabling/disabling this feature on the GPS? I'm mostly concerned with any potentially deleterious effects (getting lost if forced to switch from GPS to map)... I'll be heading out to a location that doesn't have trails (or people) so it would be nice to remove any variables that might make navigation "tricky"...

Thanks in advance (and feel free to laugh at the newbie...)!

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johnr1
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Re: Magnetic Declination - Yes or No with GPS

Postby johnr1 » Feb 01 2010 2:14 pm

I have always kept my Garmin in true since its maps as well as the paper maps are true. Removes one more source of confusion for the limited number of nuerons that I have left.

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nonot
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Re: Magnetic Declination - Yes or No with GPS

Postby nonot » Feb 01 2010 7:59 pm

In AZ it doesn't make much difference, magnetic and true north are pretty close. Unless you are going to hike in Maine or something...
http://hikearizona.com/garmin_maps.php

Hike Arizona it is full of sharp, pointy, ankle-twisting, HAZmaster crushing ROCKS!!
Hike Arizona it is full of sharp, pointy, shin-stabbing, skin-shredding plants!
Hike Arizona it is full of striking, biting, stabbing, venomous wildlife!

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Grasshopper
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Re: Magnetic Declination - Yes or No with GPS

Postby Grasshopper » Feb 01 2010 8:08 pm

nonot wrote:In AZ it doesn't make much difference, magnetic and true north are pretty close.

I thought the difference in AZ was about 11 degrees? If you were hiking a straight line being off by 11 degrees, you might end up in Maine :lol:
(Outside.. "there is No Place Like It!!")

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nonot
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Re: Magnetic Declination - Yes or No with GPS

Postby nonot » Feb 01 2010 8:26 pm

11-13 degrees.
http://hikearizona.com/garmin_maps.php

Hike Arizona it is full of sharp, pointy, ankle-twisting, HAZmaster crushing ROCKS!!
Hike Arizona it is full of sharp, pointy, shin-stabbing, skin-shredding plants!
Hike Arizona it is full of striking, biting, stabbing, venomous wildlife!

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jman1283
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Re: Magnetic Declination - Yes or No with GPS

Postby jman1283 » Feb 03 2010 11:34 am

You should by all means still use your map and compass. I find the gps screen too small to see the trail and surrounding topography even when zoomed out.

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tahosa
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Re: Magnetic Declination - Yes or No with GPS

Postby tahosa » Feb 06 2010 4:47 pm

The GPS will automatically set the declination. Now as to the compass settings, some prefer True, while some like the magnetic appeal of the compass. I use magnetic on my GPS so it talks with my basic compass. And then use a map with UTM grids at 500 meters. And scale it down to either 1:15 K or 1:10 K. And if you want to know what our current declination is then look ~here~.
AZ is nice but I still have a love for the ~back country~ of Colorado. Where I voulunteered for the USFS for 9 seasons doing backcountry patrols.

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PLC92084
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Re: Magnetic Declination - Yes or No with GPS

Postby PLC92084 » Feb 07 2010 10:38 am

Thanks, Tahosa! Appreciate the feedback. I'm using an older model Garmin (eTrex Legend); the default was Off for Magnetic Declination (MD) which is what prompted me to ask this question. I was always taught to account for MD when referencing maps; wasn't sure how that would affect my reference points when reconciling GPS and Map coordinates. I imagine for short hops (waypoint to waypoint) any error that might creep in would be negligible.

I'm still getting used to using a GPS unit so I'll continue to reference paper as my primary source of guidance in unfamiliar settings for the foreseeable future...

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nonot
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Re: Magnetic Declination - Yes or No with GPS

Postby nonot » Feb 07 2010 1:16 pm

PLC, in my experience, the magnetic compasses on the etrex's is fairly inaccurate and worrying about magnetic north offset is not high on the list of the compass troubles. I would recommend if you enjoy the challenge of navigating by compass that you continue to do so with a real compass. I suspect you already have one, but if not, most high quality ones can be purchased for $10-15, which is far less than the Garmins.

I have found that navigating by graphical GPS map, with the map set to always point north, has relegated my compass to backup duty in the event my GPS fails completely.
http://hikearizona.com/garmin_maps.php

Hike Arizona it is full of sharp, pointy, ankle-twisting, HAZmaster crushing ROCKS!!
Hike Arizona it is full of sharp, pointy, shin-stabbing, skin-shredding plants!
Hike Arizona it is full of striking, biting, stabbing, venomous wildlife!

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PLC92084
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Re: Magnetic Declination - Yes or No with GPS

Postby PLC92084 » Feb 08 2010 7:54 am

Thanks, nonot... I don't plan on using the Garmin's compass function, extensively, just for the reason you mention. I'll primarily be using the mapping function and uploaded tracks I've made for the areas I'll be exploring. What started me on this thread was the question of accuracy between coordinates/tracks shown on a GPS unit versus locating those same points on a paper Topo map. If one forgets about MD, map points are map points. Topographical features aren't going to change (if they do, we sure as heck aren't going to be hiking in that seismically-active area anyway...). Batteries and electronics fail; I just don't want to put all my eggs in one basket and wind up a couple short of an omelette...


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