UTM Coords Explained

What I understand of the UTM format (being the same as MGRS) is this:

Think of it as if you're looking at a paper mapsco book.

(This isn't literal, but makes it practical)

MM 12345 67891

MM = page

123 = Squares down the page

45 = meters down the '123' square

678 = Squares across the page

91 = meters across the '678' square

They may give you MM123678. This gives you the grid but not the exact point within that grid, which is fine because it's only 99 meters.

If the coords were MM 12345 06789 they may give you MM12367 because they drop the leading zero from 067. You must still enter the 0 before 67 when entering into the CDU.

You can enter UTM into your CDU by switching from L/L (lat/long) mode to UTM mode with LSK R9 (bottom right key). Then by entering the UTM coords in ten number, six number, or less, and selecting LSK L9 (bottom left key) to save them to the waypoint currently showing on the CDU.

For more info see Military Map Reading 201 at the Geo-spacial Intelligence Website.

Someone close the gap if I'm leaving something out, please.

See this post for an explanation (without the graphics).

• UTM and MGRS are not the same. MGRS is an overlay on UTM, making the coordinate format more manageable by dividing the large UTM grid zones into smaller, alphanumerically designated 100,000 m grid squares, thereby significally cutting down on the number of digits needed for a position reference over the radio and the potential for misunderstanding.
   
   
  
• You need to make sure that the double character grid square (e g WC, MM, DS) and grid zone designator (number plus character, e g 38T), are correct as well as the coordinates. I think JTAC typically omits the grid zone, just assuming everyone to be on the same page so to speak. Typically, you pre-brief which grid zone you're in (at least where I'm at) so it can be safely omitted unless you're operating right on the border between two grid zones and have different charts. But as Napoleon said, anything important in a war will happen between two chart sheets.
   
   
  
• Remember to truncate rather than round. Eg let us say that the MGRS for the dot following "Gusconade R" in the graphic is at approximately MGRS XC086397 (which is not quite true, as far as I can see, but it needs to be for the example to work). With lower, more realistic precision, it'd be XC0839, rather than XC0940. A grid point always means the referenced object is in the grid square east/north of the point.
   
  In the graphic, the point used could be described as, with decreasing precision,
  WC8081751205
  WC80815020
  WC808512
  WC8051
  WC85
   
   
  
• The 0 in 067 can NOT be dropped. No way, never. DCS drops leading zeroes on the eastings. This is a bug, which always gives incorrect coordinates and which can give unusable coordinates if there are two leading zeroes. To use coordinates with leading zeroes dropped in the CDU, you need to reinsert the missing zero. Odd number of digits -> Assume missing leading zero. Double leading zeroes missing? You have no way of knowing something is amiss and you're basically screwed.
   
   
  
• Regardless of the number of digits, it's still a grid square. The number of digits determines the size of the grid square indicated, or the uncertainty in the position reference.
  

• The 0 in 067 can NOT be dropped. No way, never. DCS drops leading zeroes on the eastings. This is a bug, which always gives incorrect coordinates and which can give unusable coordinates if there are two leading zeroes. To use coordinates with leading zeroes dropped in the CDU, you need to reinsert the missing zero. Odd number of digits -> Assume missing leading zero. Double leading zeroes missing? You have no way of knowing something is amiss and you're basically screwed.
  

Hi, have we heard anything about a fix coming up for this?

Not that I've heard of, but I haven't really followed the discussion either. Haven't verified the bug myself, but seen others report it.

I think my brain just exploded...

I think my brain just exploded...

:megalol: I'm with you...

Sorry guys. Rest assured that it is not at all complicated. The linked document is well worth a quick read. Fifteen minutes, and it will all come clear to you. If it doesn't, I'll instruct over MSN if need be - that's how confident I am in you really getting it. :)

The world is divided into large grid zones. They're given a number from 1 to 60 based on their east-west position (longitude) and a character based on their north-south position (latitude).

You can then give any coordinate as a combination of a grid zone and the distance east and north from the southwestern corner of that grid zone (it's really a bit more involved, but that's the general idea). 38T and two longish figures, for example. This is the UTM system.

However, UTM is rather unwieldy to work with, especially if you are out in the field trying to call in arty support over the radio, or in an aircraft trying to communicate the position of a target or friendlies on the ground. To make it easier, the MGRS was introduced. Each grid zone is divided into a large number of 100.000 by 100.000 meter grid squares. These grid squares are given designators based on their north-south and east-west position within the grid zone, using one character for north-south and one character for east-west. AM, MM, DL etc.

Now you can point out an arbitrary 100.000 by 100.000 meter square anywhere on the planet, using a designator such as 38T ME.

From there, we just need to be able to designate a certain smaller square within that square, in order to point out targets. You do this just in the same way as you did within the grid zone using UTM, by measuring the distance east and then north of the southwestern corner of the grid square.

As the square is 100 km across, you need two figures per coordinate (east/north) to give 1 km precision (0-99 km east/north of SW corner). If 10 km precision is enough (unlikely ;)), you only need one figure. The first ten km east/north of the SW corner is then 0, the next ten 1 etc.

For pointing out targets, you will generally need to get down to ten meter squares. As there are 100.000/10 ten-meter squares to each side of the 100.000 m two-character grid squares, you then need four digits (0-9999) for the easting, and another four for the northing.

For one meter precision, you need five digits.

A full MGRS coordinate consists of the grid zone, grid square and finally the easting and the northing written together as one long string of digits. Frequently, the grid zone is omitted once it is assured that everyone else is using the same grid zone.

38T ME04586742

would mean a ten meter square (four digits for easting/northing respectively) within grid square ME in grid zone 38T.

To find the position, you'd divide square ME into ten meter squares and find column 458 from the western side. Then you'd find row 6742 from the southern edge of square ME. In reality, there are supporting lines in the maps making finding these coordinates easy. You're really finding a point 4580 m to the east and 67420 meters to the north, and then you know the object for which the coordinate is given to be in the 10 by 10 m square to the NE of this point.

Clear as mud? Didn't think so. Go read the PDF and look at the graphics. Told you it's worth it. :)

Edit: Cleaned this up a bit and added a few explanatory graphics over here.

This has to be the most concise, easy to understand and dead-on accurate explanation of the MGRS I've come across. Thanks, effte, for taking the time - I am sure many a DCS Hog pilot will benefit from your effort.

Dude.. that's why I linked the doc. This post was targeted toward practical, not technical. I color coded the post and made it as simple as possible.. THEN provided the doc for people that want to go further.

The post that you linked that is supposed to explain it better is vague, but thanks for reminding me to mention that you have to re-add the leading zeros before entry into the CDU.

I was Director of Technology for a company with a 3TB geo-spacial database.. I didn't post this to display my intelligence, but rather to provide quick understandable information (mostly so I wouldn't have to answer the question in multi-player three times a day :) )

God Dammit! i dont need to know how it works, i just need to know how to work it.

God Dammit! i dont need to know how it works, i just need to know how to work it.

Which is what StrongHarm's original post was all about. With the explanations of MGRS in this thread I think I can now more easily, and certainly more quickly, relate a grid reference to a spot on the map.

Fifteen minutes, and it will all come clear to you. If it doesn't, I'll instruct over MSN if need be - that's how confident I am in you really getting it. :)

very generous offer. Thanks.+1

...now if I can only figure out MSN. :)

Reps to both of you! Great work.

Mad rep Strongharm; You should teach land navigation to the new Lieutenants in Quantico, VA!

UTM precision = MGRS precision

See this post for an explanation (without the graphics).

 

• UTM and MGRS are not the same. MGRS is an overlay on UTM, making the coordinate format more manageable by dividing the large UTM grid zones into smaller, alphanumerically designated 100,000 m grid squares, thereby significally cutting down on the number of digits needed for a position reference over the radio and the potential for misunderstanding.
  

Simply wrong! UTM is numerical and the original reference system and has been adopted to military use introducing alphanumerical description, that is why GPS, TADS and CDU say UTM.

You're mostly correct, it eases communication, eliminates misunderstandings etc., but it is basically the same system and dead accurate down to the 1 meter square.

From the document in this post, which you should read not just link :smartass::

Coordinate Comparison

UTM Coordinate – 18 367,890mE 4,243,210mN (1 meter square)

MGRS 0 digit coordinate – 18SUH (100,000 meter square on the ground)

MGRS 2 digit coordinate – 18SUH 6 4 (10,000 meter square)

MGRS 4 digit coordinate – 18SUH 67 43 (1,000 meter square)

MGRS 6 digit coordinate – 18SUH 678 432 (100 meter square)

MGRS 8 digit coordinate – 18SUH 6789 4321 (10 meter square)

MGRS 10 digit coordinate – 18SUH 67890 43210 (1 meter square)

MGRS is simply a more precise and milspec way of conveying the UTM grid. There is no MGRS grid. MGRS is to UTM what U.S. military brevity is to the english language.

+1

EricJ, could you give us a brief view of what's important to JTAC?

About EricJ

 

Occupation

US Army Joint Forward Observer

+1

 

EricJ, could you give us a brief view of what's important to JTAC?

Having the correct fills!!!! Am I right or what, EricJ? ;)

Sorry for the derail. Thankfully the game doesn't model encrypted commo. :D

Having the correct fills!!!! Am I right or what, EricJ? ;)

 

Sorry for the derail. Thankfully the game doesn't model encrypted commo. :D

Pah, crypto never causes anyone any problems ever. It always works exactly as the contract spec say it does. :megalol:

Simply wrong!

 

...

 

it is basically the same system and dead accurate down to the 1 meter square.

 

Coordinate Comparison

UTM Coordinate – 18 367,890mE 4,243,210mN (1 meter square)

MGRS 0 digit coordinate – 18SUH (100,000 meter square on the ground)

 

...

So, when I say they are not the same it is "simply wrong!", but they are only "basically the same". Finally, the two systems which are apparently the same can be compared? Hmmm.... :smartass: :D

Not convinced? What's the latitude limits of UTM? What are the latitude limits of MGRS?

Is UPS and MGRS the same? ;)

Then there's the whole ellipsoid deal as well, not sure if UTM and MGRS have always agreed there... but these days, both are based on WGS84 to the best of my knowledge. Happy to be corrected there though - I never use either in situations where it matters, so I haven't bothered to check facts.

No you always give the grid zone designator regardless of where you or where your target is on the map. No sense in breaking a habit out of laziness and working yourself into a fratricide situation because you didn't feel like saying two letters phonetically.

In my army, it's OK to drop the grid zone if it can not in any way cause misunderstandings. That essentially means having pre-briefed the grid zone in effect, and everything happening exclusively in that one pre-briefed grid zone. Amen to professional disagreement.

However, there's this little publication from the NGA. Check §3.5, beginning "all elements of a grid reference need not be used". You can in fact drop the square designator as well, if deemed appropriate and safe. :)

Cheers,

Fred

Joking aside, if you have it in writing (for public release) that the USAF mandates explicitly stating the grid zone, you should make the reference available to ED. If that's the case, the DCS JTAC needs to be updated.

<snip>

 

However, there's this little publication from the NGA. Check §3.5, beginning "all elements of a grid reference need not be used". You can in fact drop the square designator as well, if deemed appropriate and safe. :)

Nice find - suggest you add a reference in the "A-10C manuals and documents collection" sticky thread.

Totally agree

So, when I say they are not the same it is "simply wrong!", but they are only "basically the same". Finally, the two systems which are apparently the same can be compared? Hmmm.... :smartass: :D

Totally agree! :thumbup: ...intention was to help the noobs to MGRS / UTM to understand that "they don't switch from UTM to MGRS", some guys seem to mix up L/L, UTM and MGRS :huh:

So to make it precise: MGRS is a "better way" (for military purposes) to address the same grid as UTM.

In my army, it's OK to drop the grid zone if it can not in any way cause misunderstandings. That essentially means having pre-briefed the grid zone in effect, and everything happening exclusively in that one pre-briefed grid zone. Amen to professional disagreement.

...it's like telling a sniper "Left upper window of the red house on Elm Street, Arlington, USA, Planet Earth" when you are both looking through the same window of the house opposite to the red one :megalol:

All this info is good... But do I really need to know this grid system inside out?

I mean.. all I have to do is to punch in the coords in UFC right? The hogs' TAD should take care of the rest.. right?

I tried to keep the OP simple and relevant, with a deeper view through the linked doc... but Noooooooo! :)