Back to Basics: Latitude and Longitude (DMS, DD, DDM)

The position of an object, a target or a waypoint on the planet can be represented in many ways. In DCS, the simplest and most common way to define them is by means of latlongs, short for Latitude and Longitude, as they are cross-faction (imperial vs metric, east vs west), cross-module and they should sound familiar already.
By using latitude and longitude, for example, a Ka-50 FAC/A can share the location of a target with an A-10C although they have very little in common (no datalink, different system of measurement, etc).

Latitude and Longitude can be represented in different ways and players should make sure that a common format is used. This is not always a priority: a waypoint in the F-14 flight plan can be slightly more to the North or the East than its precise original location with little negative effects. If precision ordnance guided by means of GPS is employed, we better make sure that the target location is instead very accurate.

DMS vs DD vs DDM

Latitude and Longitude, being references on a sphere (not a proper sphere, but let’s keep this simple) are the offset in degrees from a common reference meridian and parallel.
The following are three common means of representing latitude and longitude.

DMS – Degrees, Minutes and Seconds
Classic representation of latlong coordinates, pretty much understandable by everyone. If you are wondering what time units of measures do in this discussion, have a look here.
DMS use North/South, East/West explicitly to indicate the direction of the offset from Greenwich and the Equator (e.g. 45°45’32.4″N 009°23’39.9″E).

DD – Decimal Degrees
Decimal Degrees are a very simple way to represent coordinates.
DD coordinates can be obtained from DMS by:

1. Carrying over the Degrees;
2. Dividing the Minutes by 60;
3. Dividing the Seconds by 3600.
4. Adding the results of point #2 and #3.

DD uses mathematical operators, plus and minus, to indicate the offset from the common references (e.g. 64.041385, -16.181383). This makes DD different and recognizable and, since this format can be represented by a simple pair of Float values, a great choice for IT/software applications.
Although DCS does not support DD latlong coordinates, this format is widely used and common.

DDM – Degrees, Decimal Minutes
DMS sounds like a combination of the two: it uses Degrees, followed by Minutes and Decimal of minutes, rather than seconds. Since DMM and DMS look similar, they can be confused quite easily.
DDM is recognizable as the seconds are represented as decimals of minutes rather than sexagesimals, and their typical indicator (quotation mark: “ ) is absent.
Converting from DMS to DDM is quite simple:

1. Carry over the Degrees;
2. Carry over the Minutes;
3. Divide the Seconds by 60.
4. Add the results of point #2 and #3.

A Practical example

The following are the coordinates of a TACAN station, displayed using different formats:
DDM= N41°36.36 E041°36.00;
DMS = N41°36’21.6″ E041°36’00”;
DD= 41.606 041.6

The difference between DDM and DMS seems minimal but, as mentioned above, if precision is required, then the correct format is necessary. For the sake of testing, I calculated the distance between:

• DMS N41°36’36” E041°36’00”
• DMS N41°36’21.6″ E041°36’00”

The result is ~450m. Albeit a minor distance, imagine updating the INS or dropping ordnance with such an error. The former case may cause a greater imprecision than expected, the latter may cause unnecessary collateral damage, failing the mission or even hitting friendly troops.

Coordinates in DCS

Different modules and even different components and devices may support one or more formats (such as the PVI-800 and the ABRIS).
The format of the coordinates can be cycled in the F-10 map by pressing, by default, [LALT]+[Y]. The default format can be selected in the Options menu (more information in the DCS manual, page 46).

The following are the available coordinate formats in DCS:

• Precise Lat/Long: very precise representation of the coordinates, up to 1/100 of second by reporting decimal seconds as well;
• LatLong DMS: discussed above;
• Metric: absolute X/Y coordinates;
• LatLong DDM: discussed above;
• NATO MRGS: acronym for Military Grid Reference System.