True or Magnetic? Degrees of variance setting?

[BrooksHD]

What is the default standard for navigation, True North or Magnetic North? How is it related to setting degrees of variance according to your actual Latitude location?

 

Some aircraft and many automobiles use a GPS. The ones I use allow changing map datum and coordinate format (h ddd mm.mmm) but I'm not aware of any settings for True or Magnetic. Modern GPS automatically adjusts time so I must assume that it uses latitude position. My handheld Garmin etrex has a default of h ddd mm.mmm, map datum WGS 84, Statute units, magnetic north reference and my current position W093 20.441' tells me that the variance is 001 degrees E. Does this sound right?

[+GeoTrekker26]

What is the default standard for navigation, True North or Magnetic North? How is it related to setting degrees of variance according to your actual Latitude location?

 

Some aircraft and many automobiles use a GPS. The ones I use allow changing map datum and coordinate format (h ddd mm.mmm) but I'm not aware of any settings for True or Magnetic. Modern GPS automatically adjusts time so I must assume that it uses latitude position. My handheld Garmin etrex has a default of h ddd mm.mmm, map datum WGS 84, Statute units, magnetic north reference and my current position W093 20.441' tells me that the variance is 001 degrees E. Does this sound right?

 

For Geocaching(registered),the only time you need to be concerned about true vs magnetic is when you are projecting a waypoint, and hopefully, the CO will tell you which to use if the distance is long enough to create a significant difference.

[+ecanderson]

The only time you'll use a reading against magnetic north is if the source information specifies that you need to do so. That could be information in a geocache, or could be directions previous taken with a compass, or ...

Normal navigational use of any GPS these days will be expressed in degrees TRUE. It saves everyone from having to dink around with local declination that varies from year to year.

[+niraD]

Yep. The only times I use magnetic north are when I'm creating or following a compass course intended for a traditional magnetic compass, or when a multi-stage geocache specifies magnetic north. All other times, I use true north.

[+MtnMutt-ProDuckShins]

NOAA, has a great site to help with Magnetic Declination ... http://www.ngdc.noaa.gov/geomag/declination.shtml

 

If you plan on using a map & compass, which would make for an interesting Puzzle Cache.

[+Joe_L]

But going back to the original question: "What is the default standard for navigation, True North or Magnetic North?"

 

There is no standard definition for “navigation”, so there is no default standard. In the context of geocaching which is tied into longitude and latitude inputs and outputs from a GPSr, then “north” is true north and navigation instructions, problems, puzzles, and references are to true north. (or at least they should be.)

 

In the context of hiking and orienteering which is tied into map and compass, then magnetic north is the most relevant because one is navigating with a magnetic compass and one needs to know the declination for the area and how to account for that with their map.

 

The use of true north or magnetic north depends on the situation, and you need to know your audience. It is very important that if someone needs to use the term “north” (or any bearing or cardinal direction for that matter) that they understand the different definitions and unambiguously convey their meaning.

 

Joe

[+EScout]

With regard to geocaching, those caches with Projection of waypoints or navigation should tell you whether to use True or Magnetic. Other issues to consider are the age of the cache and of the firmware in your GPSr.

When I placed my first multi-cache with Projections (3 total) in 2003, the local Declination was 13.33 degrees E. Now it is 12.11E. I set these caches using True North.

My first GPSr, bought in 1997, has firmware that calculates Declination, which at the time was local 13.76E. Some GPSrs let you set the Declination to update for changes over time.

If you want to see what Declination your GPSr uses in your area, look at the direction to a waypoint in True, then convert the setting to Magnetic and subtract Mag from True. If result is positive,then you have East Declination. Some GPSrs do not show fractional degrees, so for more precision, use Mils and convert to degrees: Mils difference times 360/6400= Declination in Degrees.

 

http://www.ngdc.noaa.gov/geomag-web/#declination

[+hzoi]

The standard I have seen to date for geocaching is true north. It's also been the default setting on all the GPS receivers I've used to date, but I know you can change the default setting to magnetic, at least on my Garmin fenix2 watch. I'm sure it's the same on my Montana.

 

I can think of only a handful of cases that I've seen multis that required projection using magnetic north.

 

I haven't messed with magnetic north since the last time I did a land navigation exercise, which I believe was as a lieutenant in the Armor Officer Basic Course.

 

Magnetic north is only as good as the map print date. The magnetic poles do move, and there has been significant movement north since 2000. Here's a map of how it's shifted over the years.

Edited March 15, 2016 by hzoi

[BrooksHD]

Thank you all for your input. Your answers, advice and links were all very helpful and you all obviously know what you're talking about. Nobody stated anything that conflicted with others. You guys rock!

 

I'm going to use this community and forums until they get sick of me! [] I joined as a basic member in 2009 then last Sunday upgraded to a premium member and ended a 1249 day slump with a find.! I'm back in the game and eager to learn! I wonder why my profile in the forum posts doesn't show my image or reflect that I am a premium member. Perhaps one of you may steer me in that direction. Better yet, I'll learn to navigate this forum system.

 

Back on topic and a remotely related side note: My '97 Tahoe (297,000 miles) has a mirror which displays the heading in general (N, NW, E, SE, etc) which was way off according to my sense of direction and confirmed by my Garmin Gadget family. I live in MN and after playing with the mirror it displayed the numbers 1 through 12 which I assumed to be degrees variance. Off the top of my head I think my location is 3 degrees from magnetic north. I set that and it wasn't accurate. I fiddled with it and found that setting the number to 6 produced accurate readings. ?? I am moving back to Montana in a week so I will see how it is affected.

 

Thanks again.

Trails.

BrooksHD

[+The A-Team]

I wonder why my profile in the forum posts doesn't show my image or reflect that I am a premium member.

If you log out of the forums and log back in, it should update.

 

Back on topic and a remotely related side note: My '97 Tahoe (297,000 miles) has a mirror which displays the heading in general (N, NW, E, SE, etc) which was way off according to my sense of direction and confirmed by my Garmin Gadget family. I live in MN and after playing with the mirror it displayed the numbers 1 through 12 which I assumed to be degrees variance. Off the top of my head I think my location is 3 degrees from magnetic north. I set that and it wasn't accurate. I fiddled with it and found that setting the number to 6 produced accurate readings. ?? I am moving back to Montana in a week so I will see how it is affected.

In the contiguous US, the magnetic declination varies (currently) between approximately +16° and -16°, which isn't much when considering that the resolution of the mirror's compass display is only every 45°. The fact that you say it's "way off" tells me the difference is much more than could be explained by magnetic declination, so I'm not so sure that's what that setting is for. Further, declination can be positive or negative, so the options 1-12 don't seem to fit.

 

BTW, based on the location you've set on your profile (Coon Rapids, MN), the current magnetic declination is only +0° 20', or 0.33°, which is negligible. You could go out with a magnetic compass and your GPSr set to true north, and it would be difficult to see any difference, and you could get away with doing short projections without taking it into account. However, when you move to Montana, there'll be a declination of between +8.5° and +15° (depending on where you are in the state), so you'd see more of a difference and would have to be more careful about taking it into account when projecting a waypoint.

[+ecanderson]

I live in MN and after playing with the mirror it displayed the numbers 1 through 12 which I assumed to be degrees variance. Off the top of my head I think my location is 3 degrees from magnetic north. I set that and it wasn't accurate. I fiddled with it and found that setting the number to 6 produced accurate readings. ?? I am moving back to Montana in a week so I will see how it is affected.

The 1~12 are not degrees. Rather, they are somewhat arbitrarily defined numbers for 'zones' identified for degree of correction needed based upon location, and are explained in the owner's manual for your vehicle as overlaid on a map. A "6" is the midpoint for only the very slightest negative correction, close enough for government work in your area where the declination is almost nil to begin with.

[+on4bam]

Around here (Belgium) the magnetic declination can also be ignored but when on holiday in Greenland in 2014 we noticed that North was in reality 30°. A projection with this kind of deviation would mean you're way off

So far I have not seen any caches that required to use magnetic North for any calculation.

[+ecanderson]

We have a few here where the owner decides to get 'cute' and make the puzzle or projection a bit more difficult. For example, you get something that must be converted from UTM with a magnetic north projection thrown in. Hearkens back to the old days of a map and compass, I guess. That said, I can probably count on both hands the number of times I've had to change my Garmin over to Magnetic in the field to find a multi that worked that way.

[+Markwell]

http://markwell.us/geofaq.htm#truemag

 

Magnetic North is only really required when you're following a magnetic compass. If your GPS is set to True North, and it says to go 15°, and you pull out your magnetic compass and shoot a bearing of 15° - you may be in trouble based on your position on the type of map to the right (this is an old one). However, if your GPS tells you to go 15° and you follow the arrow on the GPS (and the numbers get smaller) you'll be fine.

[+MtnMutt-ProDuckShins]

Very nice page of information you gave out... Thanks.

[+The A-Team]

That said, I can probably count on both hands the number of times I've had to change my Garmin over to Magnetic in the field to find a multi that worked that way.

Unless the cache is very new or you live in an area with negligible declination, you'd rarely want to just go out and use a magnetic compass (whether standalone or in your device), because the magnetic north pole moves around and the magnetic declination changes over time. "Project a waypoint 500 metres at 24° magnetic" on a cache placed in 2005 will probably mean something totally different today. The best way to handle such cases is to use a historical declination calculator to determine the declination at the time the cache was hidden (the Canadian government has a good one I've used many times), then convert the bearing to true north. Once you do that, you can happily use this new bearing with whatever projection method you typically use, or convert it back to magnetic again using today's declination and use your compass.

[+on4bam]

Another nice site to know the deviation from true North.

[+ecanderson]

That said, I can probably count on both hands the number of times I've had to change my Garmin over to Magnetic in the field to find a multi that worked that way.

Unless the cache is very new or you live in an area with negligible declination, you'd rarely want to just go out and use a magnetic compass (whether standalone or in your device), because the magnetic north pole moves around and the magnetic declination changes over time.

Yes, ref post #3, "It saves everyone from having to dink around with local declination that varies from year to year."