Converting GPS positions
June 04, 2013 at 11:00am
Captain Paul's Response to ~ Bluewing~
The position you listed is NOT stated correctly.
A position of Degrees, minutes and seconds which i believe that is what it is, should be shown as 29° ( for degrees) 18' (for minutes) and 25'' (for seconds). The ('') means seconds and not inches.
This is a regular GPS position format (DDD,MM,SS). Most GPS units can express a longitude-latitude position as shown above and as decimal degrees expressed as DDD.dddddd and as Degrees, minutes and thousandths of minutes expressed as DDD,MM.mmm.
All of these are different ways to state the same position. If you are trying to convert your DDD,MM,SS position to a position of DDD,MM.mmm, then here is a pointer or two:
If The first position is in DDD,MM,SS. meaning Degrees, minutes, and Seconds. Some units also allow a decimal seconds format which would be written as DD,MM,SS.s and you want to convert it to a position that is written as Degrees, Minutes and thousandth of minutes. (DDD,MM.mmm) Which is the most commonly used format for Latitude - Longitude positions in most GPS units, then consider doing either of these two procedures:
First, Most GPS units have a setting in the menu, usually in the set up or navigation screens that allow the user to configure their unit in Decimal Degrees (DDD.dddddd),
Degrees, Minutes and Seconds and tenths of seconds (DDD,MM,SS.s) And a format of Degrees, Minutes and thousandths on minutes (DDD,MM.mmm).
You can change the present format for latitude-Longitude positions to any of the existing formats and the GPS unit will convert the values for the positions to the newly selected format. You can change the format to DDD,MM,SS, enter the position and when finished, changed back to your standard position of decimal minutes.
Secondly, Remember your high school math, where there are 60 seconds in a minute, sixty minutes in a degree, and 360 Degrees in a circle. Armed with that knowledge you can mathematically convert one format to another.
First remember that the degrees will be the same if you are only converting the decimal minutes to seconds or the reverse.
Here is where the 60 minutes and seconds come in the play.
To convert seconds to minutes, you would divide the seconds by 60. For instance,
90 degrees, 30 min and 45.1 sec divided by 60 = .0751666 minutes. Rounded off to three decimal positions the converted value would be 90 degrees, 30.075 minutes. If The position were in decimal minutes (DDD,MM.mmm) and you wanted to convert it to DDD,MM,SS, you would MULTIPLY the decimal part on the minutes by 60.
For instance, a position of 28 degrees 45.200 seconds would convert to 29 degrees
45minutes and 12.0 seconds.
If you have a number of positions to convert, It is easier to change the POSITION FORMAT in the unit and then enter the DDD,MM,SS position.
Remember when doing the math, that you must do both the latitude and longitude for each position.