"Military magnetic north"?

[timz2]

In another topic somebody said "My gpsr also has military north and military magnetic north."

 

Is there more than one kind of magnetic north?

 

"Military north"... that must be UTM-grid north? If so, do GPS's really call it that?

[+Timpat]

On my Garmin units there is a choice under Setup/Heading (I think it is) for Mils, which is used by the military, and can be Magnetic or True. Maybe this is what you're referring to. There is 360° in a circle, or 6400 Mil. One degree is about 17.8 Mil. I use Mil if I want to project a point to a greater degree of accuracy over a long distance.

[roybassist]

In another topic somebody said "My gpsr also has military north and military magnetic north."

 

Is there more than one kind of magnetic north?

 

"Military north"... that must be UTM-grid north? If so, do GPS's really call it that?

You can set your coordinate system to MGRS, Military Grid Reference System. If you then set your North Reference to Grid, north would be based on the military grid. I think the person who called it military magnetic north was confused.

[+trainlove]

Yes, it's Grid North and has nothing to do with either Geographic or Magnetic North.

 

The MGRS ir UTM grids are oriented with True/Geographic North only along the basis meridian, but can be up to about 2 degrees off (or about 35Mils) off from True North if you are at the edge of a zone like me between zone 19 and 18. I think it can get really far off, but only for polar bears way far north or south, but I've never seen it more than 2 degrees.

[Alex n Daddy]

The other neat thing about MILs is... they're metric.

A mil is 1 metre, taken out to 1 kilometre. If you had a freind with a meter stick, and he stood 1 kilometre away, your viewing angle from one side of the stick to the other would be one mil.

If you took 6,400 meter sticks, put them on the ground head to tail, with an angle of 1 mil between each, you'd wind up with a circle.

Degrees are cool too... 365 days in a year, 360 degrees in a circle. A degree is the distance the sun moves against the background stars every day (to within 5/360 of accuracy).

[+trainlove]

The other neat thing about MILs is... they're metric.

A mil is 1 metre, taken out to 1 kilometre. If you had a freind with a meter stick, and he stood 1 kilometre away, your viewing angle from one side of the stick to the other would be one mil.

If you took 6,400 meter sticks, put them on the ground head to tail, with an angle of 1 mil between each, you'd wind up with a circle.

Degrees are cool too... 365 days in a year, 360 degrees in a circle. A degree is the distance the sun moves against the background stars every day (to within 5/360 of accuracy).

Well that's actually only approximate. But is the whole reason for it in the first place. Much easier to use than 'milli-radians'.

 

The military rounded 2*PI*1000 which is 6283.185307 to the nice round 6400. But doing what you describe is only 1.8% off.

 

http://en.wikipedia.org/wiki/Angular_mil is very informative about the 'different' Mil's.

Edited December 6, 2008 by trainlove

[+Cstandi1]

Even the military doesnt use mils much. For normal land nave we stick to degrees. Mils are for when you need to be really accurate like calling in artillery. And even UTM and MGRS are different, they are the same basic idea but dont try interchange them, bad things will happen. Grid North is simply explained as straight up on a map. The grid refers the MGRS grid laid on on the map.

Edited December 7, 2008 by cstandi1@utk.edu

[7rxc]

Even the military doesnt use mils much. For normal land nave we stick to degrees. Mils are for when you need to be really accurate like calling in artillery. And even UTM and MGRS are different, they are the same basic idea but dont try interchange them, bad things will happen. Grid North is simply explained as straight up on a map. The grid refers the MGRS grid laid on on the map.

 

I guess it depends on what military, and what section... NATO uses mils, Canada sure does... Air tends to use degrees, same for Maritime. Mils are used for artillery, but in the time before ... way back... it was not uncommon to read degrees, minutes, seconds... even Radians depending on what you had available to measure with... its more in the execution of the measurement. UTM and MGRS are both different and the same... it is exactly the same grid... 1 km squares at 1:50000.. the prime difference is the method of designating the grid reference... UTM zone and block number followed by the eastings and northings for one

and the 2 letter block identifiers plus eastings and northings for MGRS. With UTM there is a more frequent reuse of numbers, thus more blocks and zones... less chance of critical duplication errors with MGRS but then you have to make sure some people can read two letter codes correctly or the numbers get out of sorts. As someone else said the grid NS lines point to true north ONLY along the center meridian of a UTM zone... otherwise there is an offset known as covergence of meridians... that has to be dealt with... near the equator, it isn't as great as more poleward... up here between 49 and 51 N lat... the convergence angle is about .75 degrees per degree east or west of the central meridian... never more than 2 and a bit degrees.

This changes with the distance north / south of the equator since the width of a degree of longitude decreases as you get up toward the poles. We use about 1.4 degrees E. Grid north is thus seldom True North... as for Magnetic North, that moves around and is corrected using declination. Magnetic Declination is measured from Magnetic to True North, Grid Declination is measured from Magnetic to Grid North.

 

Doug