Garbage in, garbage out: My UTM data entry in CDU is all messed up

[Bahger]

I took a long break, now some things are easier to re-learn than others.

 

In inputting UTM coordinates given to me by a JTAC, I can't seem to get it right. The JTAC gives me LN 745176. However, it seems to me that the UTM coordinates in the CDU for flightplan wps have more digits (2 groups of 4) after the two letters. When I enter the above coordinate it's always way wrong.

 

I don't think it's about being in the wrong UTM zone. What am I missing?

[cichlidfan]

I am not an expert on any of this but I do collect good notes. I grabbed this info from the forum quite some time ago but to the best of my knowledge it is still correct.

 

Hope it helps.

 

Btw, you are supposed to enter the letters as well as the numbers. That gets you eight characters.

JTAC UTM data entry in CDU.pdf

[Quirkitized]

They round to the nearest third digit.

 

Also, nearly all flights in available areas with towns, airfields, etc are either 38t or 37t. Jtac does not give this info in the 9line. So if you are flying in 37t, and he gives you coords but they are way off, try putting 38t in, then the coords, or vice versa.

 

For instance if a unit is at 38T AB 123159 320784

JTAC would say AB 123 321.

 

They wont say 38T. So unless you were already in 38T (your cdu would show 37 or 38T) zone, your coordinates will be way off. afaik the only way around jtac not giving grid is by having a map and knowing, or re-doing the coords.

 

So for instance the above, if u put those in and your in 37T, lets say target is 350 miles away. That wouldn't be right, input 38T, then input AB 123 321, and the target is say 30 miles away, I would assume that is the correct.

 

if this isn't the issue then nevermind :D

[HugePanic]

I would assume that is the correct.

 

I really hope this is not the way the Airforce Bombe its targets.

 

JTAC: "Go 300miles two target!"

Pilot: but thats so far way? I will not make it home for dinner then. Can i just simply bomb an other target 30miles way??"

[cichlidfan]

I really hope this is not the way the Airforce Bombe its targets.

 

JTAC: "Go 300miles two target!"

Pilot: but thats so far way? I will not make it home for dinner then. Can i just simply bomb an other target 30miles way??"

 

With respect to the scenarios typical of the sim it is correct.

[Quirkitized]

With respect to the scenarios typical of the sim it is correct.

 

haha yes, i don't think you will find many missions you will have to travel 300+ miles to hit a jtac target in the sim :pilotfly:

[Bahger]

Now I feel really stupid; I was forgetting to enter the inputted coordinates with OSB 16. Sorry to have wasted your time.

[ScottishMartialArts]

I took a long break, now some things are easier to re-learn than others.

 

In inputting UTM coordinates given to me by a JTAC, I can't seem to get it right. The JTAC gives me LN 745176. However, it seems to me that the UTM coordinates in the CDU for flightplan wps have more digits (2 groups of 4) after the two letters. When I enter the above coordinate it's always way wrong.

 

I don't think it's about being in the wrong UTM zone. What am I missing?

 

With UTM, the numeric coordinates specify a metric square of increasing precision. If you were to have just two numeric digits, such as LN 1 2 -- note that such a coordinate is so imprecise as to be useless, and thus never appears either in game or irl -- then the coordinate would be for a square that is 10,000m x 10,000m. Four numeric digits, LN 12 34, corresponds to a 1,000m x 1,000m square. Six numeric digits, LN 123 456, which happens to be the precision you work with when they teach you land navigation in the US Army, corresponds to a 100m x 100m square, which is enough to get you in sight of your objective when on foot, or enough to call for fires provided you aren't danger close. Finally, eight digits, LN 1234 5678, and ten digits, LN 12345 67891 correspond to 10m x 10m and 1m x 1m squares, respectively.

 

The CDU always expects a 10 digit UTM coordinate, but it is programmed to parse less precise coordinates. Specifically, it will treat a less precise coordinate as being the truncated version of a ten digit 1mx1m precision coordinate. In other words, the CDU will take the entered coordinate, and append the appropriate number of zeroes to make it ten digits. For example, if you enter LN 123 456, the CDU will translate that into LN 12300 45600. The CDU waypoint will therefore have a 1mx1m precision, but the actual target or location being referenced by the coordinate in this example may be anywhere in the box formed by drawing an imaginary line east 100m and north 100m from the actual waypoint. This has to do with how coordinates are read on a map with MGRS gridlines -- you go right (east) then up (north) -- and since the CDU has appended zeroes to a six digit coordinate, the waypoint is specifically for the 1mx1m location at the bottom left of the box specified by the coordinate given to you by the JTAC or whomever.

 

One last note: the digits of the coordinate must have even parity, i.e. you can have 6 or 8 digits, but not 5 or 9, etc. For example, LN 123 45, would refer to a box that has 100m precision in Eastings, and 1000m precision in Northings. Since grids, and by extension grid coordinates, are squares, you need identical precision in both dimensions. Therefore, feeding the CDU with odd parity coordinates will cause it to generate an error.

Edited March 10, 2013 by ScottishMartialArts

[Bahger]

This is very useful info, thanks for taking the time to post it here.