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, et cetera).

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 adverse effect. If precision ordnance guided by means of GPS is employed, we better make sure that the target location is 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 why time-related units of measure appear 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 points #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 recognisable, and, since this format can be represented by a simple pair of Float values, it is a great choice for IT/software applications.
Although DCS does not support DD latlong coordinates, this format is widely used and common in daily life.

DDM – Degrees, Decimal Minutes

The acronym “DDM” sounds like a combination of the two formats discussed so far: it uses Degrees, followed by Minutes and Decimal minutes, rather than seconds. Since DMM and DMS look similar, they can be easily confused. In DCS, the difference between the two is either relevant or irrelevant, depending on the context. For example, if a waypoint is defined for older INS analogue devices, such as the AN/ASN-92 or the AN/ASN-63, the INS of the F-14A/B Tomcat and the F-4E DSCG, respectively, then other factors play a more significant role in the precision of the navigation. On the other hand, if the latlongs mark the location of a target, the crew must ensure that the correct format is specified.

DDM is often recognisable 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 points #2 and #3.

A Practical Example

The following are the coordinates of Kobuleti Airport’s TACAN station (see the next paragraph):
DMS= N41°55’50” E041°51’43”;
DDM = N41°55.846′ E41°51.717′.

The difference between DDM and DMS may seem 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 as if both were considered DDM coordinates:

• DDM = N41°55.846′ E41°51.717′;
• DDM→DMS N41°55’50” E041°51’43” → N41°55.50 E041°51.43 (DMS incorrectly intended as DDS).

The result is ~750m. Albeit a minor distance, imagine updating the INS or dropping ordnance with such an error. The former case may cause greater imprecision than expected, while the latter may result in unnecessary collateral damage, potentially failing the mission or even harming 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 [LALT] + [Y] by default. The default format can be selected in the Options menu (see the DCS manual, page 46, for more information).

Pressing [CTRL] + [Y] opens a popup with more details about the cursor’s location.

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