Author Topic: Intersections  (Read 2229 times)

Lyle Brotherton

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Intersections
« on: May 02, 2012, 03:05:11 PM »
Describing accurately the bearing of a distant object not on your map

Meeting with Scott Amos yesterday, we were discussing an incident involving a light aircraft that had come down, some distance away, which was not on the OS sheet in use, and how to describe its location. I was telling him about a military technique to describe enemy positions using a map and compass.

There are three methods to employ, ranked here by time taken to perform:

Kwikfire Section
1 Identify where you are on the map
2 Sight the distant object and while looking at it, spot a feature exactly in your line of sight in-between you and the distant object that will be on your map
3 Plot a line on your map from your location to the feature you sighted
4 Using your compass measure this bearing on the map
5 Relay this bearing, your current location (grid reference) and the feature beyond the incident to control. They can now search along this line (bearing) between the two points for the incident locus.
6. If possible, perform Stereoscopic ranging to it and add this information to give to control.

Double Intersection
1 Perform the Kwikfire section described above.
2 Move off to the side of the incident at an angle of 45 different from the current bearing to the incident. This minimises the distance you need to travel before a second bearing would be significantly different to the first.
3 When the new bearing to the incident is +/- 20° different from your first, take a second bearing to it.
4 Relay your second location (grid reference) and this bearing to control, who can now plot these bearing from your locations - where they intersect is the estimated position (EP) of the incident.

Full Intersection
1 Perform the Kwikfire Section described above.
2 Radio to other parties in the area to perform a Kwikfire Section to the incident
3 Conversely perform a Double Intersection and keep moving to take a third bearing to the incident.

Note the greater the difference between the bearings taken, and the greater the number of bearings taken to it, the more accurate the results.





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Brian

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Re: Intersections
« Reply #1 on: May 02, 2012, 05:22:43 PM »
Good, useful stuff, clearly presented.  I love this kind of thinking.

It's logical, simple and easy to understand - once someone tells you how!

And it reminds me of one of my favorite anecdotes.  (Forgive me   :)  )

As the story goes, when Christopher Columbus returned from having discovered the new world, he attended a banquet.  As wine flowed, the guests began to minimize his accomplishment:  "All you did was sail west . . . if you hadn't, someone else would have . . . etc." 

So Chris removed an egg from its basket and challenged the gathering to stand it on its end without use of any implement or grains of salt.  Everyone at the table failed, and in their frustration, they all challenged him to do it.  Chris took the egg in his hand, raised it above the table, and brought it down smartly, slightly crushing one end, where it rested "on end."

"You see how easy it is, once someone shows you how?" he said.

Callum

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Re: Intersections
« Reply #2 on: May 02, 2012, 05:29:15 PM »
Yes, good technique to post, and not just search and rescue either. I can think of quite a few situations, where we have several different groups on the hill and one that we need to bring back in for some reason, but our radios (VHF) and mobile phones have poor or no reception, we can describe exactly where they are to other groups.

Any reason you did not put this in ther book?

Back in my military day, we had big plastic azimuth cards we used to place over the locations on the map, they worked well.



Skills4Survival

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Re: Intersections
« Reply #3 on: May 02, 2012, 07:17:40 PM »
interesting you are actually the object (or set of objects), normally used by the person who want to locate him/her self. What is Stereoscopic ranging? Do not get a clear answer from google.
Ivo

Pete McK

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Re: Intersections
« Reply #4 on: May 03, 2012, 07:51:42 AM »
You must have missed it Ivo at the bottom of page 169 in the UNM  ;)

So this is a reverse of a resection? Where, as Ivo says, you become the 'attack point' - clever. Agree with Callum, I can see quite a few applications for this technique in the mountains when working with groups.

Skills4Survival

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Re: Intersections
« Reply #5 on: May 03, 2012, 08:45:31 AM »
Pete, pretty lame I do not look in the most Ultimate index to find this. Will be the last time...:-)  (thanks for the pointer)
Ivo