Author Topic: Azimuth or Bearing  (Read 27544 times)

Lost Soul

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Re: Azimuth or Bearing
« Reply #15 on: November 22, 2012, 11:12:24 AM »
Thank you Barry, that is very clear.

Lyle Brotherton

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Re: Azimuth or Bearing
« Reply #16 on: November 23, 2012, 08:46:56 AM »
Barry, military traditions, as you know, take a great deal of time to change and some never do. The military units I work with in the USA all still use the terms "shoot an azimuth" or "follow an azimuth" and the quadrant system to which you refer and used back in the 50's.

The military Mil is also here to stay. I believe that this goes back to any forward soldier, calling in artillery fire, took some comfort - but not a lot :) - that there was greater precision in using the 6400 units to divide a complete circle than 360.

It was only recently, as in my working life-time, that the military in countries such as Germany and Sweden, stopped using their unique compass systems, the 400 Grads to a circle, and because NATO needs to function as a cohesive force, uniformity is essential.

In practice, I think artillery will always quote the azimuth in Mils, whereas the foot soldier will use more general terms using, N NNE NE NEE etc. (I don’t know the correct term for these)
“Opinion is the medium between knowledge and ignorance” - Plato

Callum

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Re: Azimuth or Bearing
« Reply #17 on: November 23, 2012, 09:09:40 AM »
Artillery is the term used that refers to military units firing an explosive shell (or in modern weapons rockets) only using data set on the sights, called ‘indirect fire’, as opposed to viewing the target through a sighting mechanism, ‘direct fire’. The data set on the sights is determined from muzzle velocity, temperature, wind, and air density, and since distances can often be considerable to the target, Mils are used to minimise error.

At 10km a 1 degree error represents 300m (175m either side of the target), whereas, a 1 Mil error is only 20m (10m either side of the target).

Pete McK

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Re: Azimuth or Bearing
« Reply #18 on: November 23, 2012, 11:39:04 AM »
In practice, I think artillery will always quote the azimuth in Mils, whereas the foot soldier will use more general terms using, N NNE NE NEE etc. (I don’t know the correct term for these)

I suspect that Hugh will know ;)

Hugh Westacott

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Re: Azimuth or Bearing
« Reply #19 on: November 23, 2012, 11:57:43 AM »
Oddly enough, I do!

N,E,S, & W are known as the cardinal points of the compass.
NNE, NE, & ENE etc (the intermediate points), are known as ordinal points of the compass.

It used to be the case that mariners and boy scouts had to learn the order of the points of the compass by heart ,a practice known as 'boxing the compass'.

Hugh

Pete McK

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Re: Azimuth or Bearing
« Reply #20 on: November 23, 2012, 12:06:54 PM »
Thank you Hugh :)

Hugh Westacott

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Re: Azimuth or Bearing
« Reply #21 on: November 23, 2012, 01:37:48 PM »
I was neither a mariner nor a brussel sprout (British rhyming slang for a boy scout). I was taught elementary navigation techniques by my father in the '40s using a 1:63360 map and a cheap brass compass with a wobbly needle that had a mind of its own. When accuracy is not at a premium, I still find myself saying to myself that after about 150 metres I'm looking for a path that runs approximately SSW.

Hugh

adi

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Re: Azimuth or Bearing
« Reply #22 on: November 23, 2012, 08:43:06 PM »
All of the British Army except the Army Air Corp use mils.

If i remember correctly the only time we used the term azimuth was when we were describing the angle the sun would move whilst surveying using the sun. The Americans do use azimuth as already described, it's not right or wrong it's just the fact that american English is a different language to our English.

A bearing is a bearing and not an Azimuth, an azimuth is an angle between two points a bearing is a direction.
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

adi

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Re: Azimuth or Bearing
« Reply #23 on: November 23, 2012, 09:02:33 PM »
N NNE NE NEE etc. (I don’t know the correct term for these)

They are called cardinals Lyle.
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Lost Soul

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Re: Azimuth or Bearing
« Reply #24 on: November 24, 2012, 08:48:36 AM »
Ah yes Hugh, boxing the compass I remember it well from my youth.  16 points to basic box and 32 for those with a good memory.  Anyway thanks to Barry’s post we are teasing out some interesting information.

I have another question.  Mils, a system for dividing up a circle (compass plate) into equal parts favoured by certain Armies. 

So my questions are.

When was the system invented?

By whom?

And why? 

Why is the  system called Mils?  Is this a contraction of Military, or a corruption of Milli meaning a one thousandth part?  Or something else?

Why is the circle divide into 6,400 parts?  What is the rational  for that?

Etc, etc?

Hugh Westacott

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Re: Azimuth or Bearing
« Reply #25 on: November 24, 2012, 09:51:45 AM »
I seems that my memory was a fault. I've done some more research in the light of Adi's post. A traditional compass rose has 32 named points known collectively as the points of the compass' viz:

N,E,S & W are the 4 cardinal points
NE, SE, SW & NW are the 4 ordinal points

Then it gets complicated. Here is the sequence of the named points:
1   N
2   NbE (north by east)
3   NNE (north northeast)
4   NEbN   (northeast by north)
5   NE (northeast)
6   NEbE (northeast by east)
7   ENE (east northeast)
8   EbN (east by north)

This sequence is continued for the remaining three quadrants.

The angle between each point is 11.25°.

Hugh

Lyle Brotherton

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Re: Azimuth or Bearing
« Reply #26 on: November 24, 2012, 10:08:47 AM »
Here's a brief history on the Military Mil and its difference from milliradian.

Milliradian
These are 1/1000th of a radian.
Dictionary definition of a Radian: these describe the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc and is mainly used in astronomy. One radian is the angle subtended at the centre of a circle by an arc that is equal in length to the radius of the circle.

Mil
According to British army archives the 21st Brigade Royal Artillery first proposed, in 1911, the use of milliradians as a precise method for determining the azimuth of the compass circle. However there are 6283.19 milliradians in a complete circle and in 1912 a joint Artillery body for the British Army met with their equivalent in Naval Gunnery (the Ministry of defence was not formed until after WWI). It was agreed to round up the exact milliradians to 6400 – this number was chosen as the optimal as it could easily be divided by 8 which corresponds to the primary cardinal directions Hugh has been posting about : N, NE, E, SE, S, SW, W, NW.
“Opinion is the medium between knowledge and ignorance” - Plato

Lost Soul

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Re: Azimuth or Bearing
« Reply #27 on: November 24, 2012, 01:00:19 PM »
Thanks Lyle very informative.
 
Radians, yes.   Also used extensively in physics and engineering for mathematical analysis of angular motion.  Where a full circle is described as being 2π radians.  2π = 6.283 thus giving that number of radians in a full circle; and a radian is 57.296°. 

N.B this funny mark " π " is ment to be Pi.  Strange malformation beteween a genuine Pi symbol on my computer and the copy and paste of it to the forum. 

Back to the practical.  So effectively a Mil has it origins in the Artillery seeking significant improvements in gun laying accuracy and it became the adopted standard for the Army in all things land navigation?  You mention the Navy were involved in defining the Mil.  Their navigation is and always has been based on the 360° (and boxed) compass.  So do the Navy use Mils for gun laying? 

I can see it being advantageous for on-shore batteries.   But on a vessel bobbing about on the seas as well as moving through the sea?  Bit of a tall order to try and achieve that sort of accuracy and precision that the Mil endows.

adi

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Re: Azimuth or Bearing
« Reply #28 on: November 24, 2012, 04:57:45 PM »
[Moderator comment: on the off-chance that an artilleryman reads this and acts on it, I've corrected the mils/degrees confusion; original text in [], corrected text in italics]

Lets make one thing clear we are talking about the British Mils system which is now the NATO Mil, different countries use different Mil systems, Russia being notable.

Basically there are 18 mils to 1° more accurately there is 17.777 mils to 1°.

A 1 degree deviation from a bearing over 1 Km is 18 meters or more accurately 17.777 meters this is well within the effective kill zone of an Artillery shell which differs between weapon type but for the purpose of this conversation is a radius of 75 m. And it is very rare for 1 gun to fire one round as a fire mission, normally the very least is 3 rounds from 6 guns and like with darts it is hard to have the rounds fly without some deviation in flight so they don't hit the ground  in the exact place, meaning they are an area weapon.

Depending on the charge used we could shoot up to 30 Km so a deviation of 1 degree would mean a loss of accuracy of around 540 meters add to that deviations in the fight and other tolerances the accuracy could drop to around 1 km.

This is unacceptable by any ones standards so you can start to see why the Artillery are masters of bearings and navigation. In the OP's the Artillery observers when a gun fires you expected to see the splash of the round with in the field of view of the binoculars, if you did not see the splash you would ask your team if they saw the splash without using bins if they did not something very wrong has happened. If you have not heard the round splashing then your ass was seriously on the line because the round had dropped somewhere unknown and you are never sure it has splashed safely.

[Moderator comment:

The length of a circular arc of radius r, and subtended angle, theta radians, is simply r*theta.  Now, since the mil is essentially a milliradian*, the length of a circular arc of radius r and subtended angle 1mil is r.1/1000.  So, for a radius of 1000m, the arc length is 1000*1/1000 = 1m.  This is the reason why mils are useful for artillery purposes, because the arithmetic for correcting shot fall angle is simple.

*There is a small error arising from the approximation of 6400 mil in a circle, compared with 6283 milliradians; about 1.25% error.]

Cheers CP for spotting that the second correction should be degrees because i am trying to explain the size of the error using degrees. If that makes sense. (I think, it was ages ago since i posted that)
   
« Last Edit: December 20, 2012, 12:31:27 PM by captain paranoia »
"We do not belong to those who only get their thought from books, or at the prompting of books - it is our custom to think in the open air, walking, leaping, climbing or dancing, of lonesome mountains by preference, or close to the sea, where even the paths become thoughtful." Friedrich Nietzsche

Hugh Westacott

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Re: Azimuth or Bearing
« Reply #29 on: November 24, 2012, 05:07:26 PM »
Could not greater accuracy be achieved by dividing every degree in a circle into 20 divisions? That might prevent a lot of confusion.

Hugh