Latitude/Longitude Formats and Conversion

Introduction


Terrain Navigator Pro allows you to display and enter Latitude/Longitude coordinates in three formats: Degrees Minutes Seconds (D° M' S"), Decimal Minutes (D° M.M'), and Decimal Degrees (D.D°). Each of these formats can represent the same geographic location, but expressed differently.

For example, MyTopo's headquarters in downtown Billings, Montana is located at the following coordinates:
45° 46' 52" N 108° 30' 14" W
as displayed in Degrees Minutes Seconds (D° M' S"). This same location, in displayed Decimal Minutes (D° M.M'), is:
45° 46.8666' N 108° 30.2333' W
In Decimal Degrees (D.D°), this same location is:
45.7811111° N 108.5038888° W

Which format should I use?

When Terrain Navigator Pro first starts, it displays all coordinates in Degrees Minutes Seconds (D° M' S") - as this is the most commonly used. However, many popular GPS units (such as those made by Garmin) default their coordinate systems to Decimal Minutes (D° M.M'). This can sometimes cause confusion when manually entering coordinates from the GPS into Terrain Navigator Pro. To compensate for this, change the Coordinate Preferences in Terrain Navigator Pro to match the Position Format specified in the GPS.

Some have found that the Decimal Degrees (D.D°) format works particularly well, since it is made up of a single number sequence (one for latitude, one for longitude) when transferring coordinates between applications. This is why Terrain Navigator Pro uses this format in its various file formats for import/export of layers, such as routes, tracks, markers, etc.

How do I convert between formats?

To convert from Degrees Minutes Seconds (D° M' S") to Decimal Degrees (D.D°)
Use the following formula:
Degrees + (Minutes divided by 60) + (Seconds divided by 3600) = Decimal Degrees
- or -
D + (M/60) + (S/3600) = D.D°
For example, a latitude of 45 degrees 46 minutes 52 seconds would translate to:
45 + (46/60) + (52/3600) = 45.7811111°

To convert from Degrees Minutes Seconds (D° M' S") to Decimal Minutes (D° M.M')
Use the following formula:
Degrees and Minutes + (Seconds divided by 60) = Decimal Minutes
- or -
D and M + (S/60) = Decimal Minutes
For example, a latitude of 45 degrees 46 minutes 52 seconds would translate to:
45 and 46 + (52/60) = 45° 46.86666'

To convert from Decimal Degrees (D.D°) to Decimal Minutes (D° M.M')
Use the following formula:
Degrees = Integer Portion of D.D°
Minutes = Decimal Portion of D.D° (including the decimal point) * 60
- or -
Int(D) = D°
(D - Int(D)) * 60 = M.M'
For example, a latitude of 45.781111 degrees would translate to:
Int(45.781111) and (45.781111 - Int(45.781111)) * 60 = 45° 46.86666'

To convert from Decimal Degrees (D.D°) to Degrees Minutes Seconds (D° M' S")
Use the following formula:
Degrees = Integer Portion of D.D°
Minutes = The Integer Portion of the Decimal Portion of D.D° (including the decimal
point) * 60
Seconds = The Decimal Portion of M.M (including the decimal point) * 60
- or -
Int(D) = D°
Int((D - Int(D)) * 60) = M'
(((D - Int(D)) * 60) - Int((D - Int(D)) * 60)) * 60 = S"
For example, a latitude of 45.781111 degrees would translate to:
Int(45.781111) and Int(45.781111 - Int(45.781111)) * 60 and (((45.781111 - Int(45.781111))
* 60) - Int((45.781111 - Int(45.781111)) * 60)) * 60 = 45° 46' 52"

A Note About Sign and North, South, East West

Generally speaking, Latitude/Longitude is followed by an indication of hemisphere. For example 45° 46' 52" N indicates the Northern Hemisphere (North of the equator.) 108° 30' 14" W indicates an area West of the Prime Meridian. When noting this numerically (especially in Decimal Degrees), positive and negative values are sometimes used. A positive value for North and East, a negative value for South and West. Thus, in our example, when noting 45° 46' 52" N 108° 30' 14" W in Decimal Degrees, it may appear as 45.7811111 -108.5038888 when represented numerically. This is the case within Terrain Navigator Pro various file formats for import/export of layers, such as routes, tracks, markers, etc.

And Regarding Datum...

Datum is a modifier of all coordinate systems. Be sure that the datum setting in Terrain Navigator Pro (in Coordinate Preferences) matches the datum the coordinates were gathered in. (If you are not sure, WGS84 is usually a safe bet.) The datum of all import/export formats in Terrain Navigator Pro is WGS84.

Terrain Navigator Pro handles internal data conversions in WGS84 datum, and then presents the coordinate information in whatever datum you have selected in Coordinate Preferences. When you export layers (markers, routes, tracks, etc.) from Terrain Navigator Pro, the coordinate data in the resulting export file is given in WGS84 datum and Decimal Degrees. Therefore, when creating your own layer data to import into Terrain Navigator Pro, be sure to use WGS84 datum when editing your text file. Using a datum other than WGS84 will affect the accuracy of the coordinate locations in Terrain Navigator Pro.

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