Different platforms use different formatting methods for displaying lat/lon information. There are 3 general formats that you will see. Before you do anything with the numbers, you need to first decide which format they are in. See the more detailed definitions below.
1) dd mm.mmm - This is the format favored by most GPS units. It represents degrees followed by minutes (with decimal places). 3 decimal places is standard as with DGPS, that represents about 10 foot of accuracy.
2) dd mm ss - Degrees, minutes and seconds. This was a standard for many years and still appears in many publications/notations. (May also appear without seconds, which implies 00 as the seconds.)
3) dd.ddd - Degrees with decimal places. Not widely used except in some conversion processes where the number of decimal points varies.
Ok, so once you decide which is which, how do you convert?
dd mm ss -> dd mm.mmm - Keep the dd mm part. Divide the ss part by 60, and that equals the decimal part of your minutes.
Ex. - 39 30' 45" -> 39 30.750'
dd mm.mmm -> dd mm ss - Keep the dd mm part. Multiple the decimal part of the minutes by 60 and that equals the seconds.
Ex. - 38 15.250' -> 38 15' 15"
dd.ddd -> dd mm.mmm - Multiple the decimal part of the degrees by 60 to give you the minutes including decimal points.
Ex. - 40.100 -> 40 06.000'
dd mm.mmm -> dd.ddd - Divide the minutes (including decimal) by 60 to give you the decimal part of the degrees.
Ex. - 74 15.000' -> 74.250
dd - degrees of latitude or longitude. Should include a N/S (north/south, for latitude) or E/W (east/west, for longitude) designator to tell in which hemisphere or side of the Prime Meridian (0 degrees longitude), respectively, but for most local charts, this is left off because of the "assumption" you know on which side of the equator/Prime Meridian you are (for this area, anyway). May use the "d" as shorthand for degrees, or the degree symbol (a small o as a superscript above the number).
mm - minutes of latitude or longitude. There are always 60 minutes in a degree of latitude or longitude, however the distance that a degree represents differs for lat and lon. 1 minute of latitude is equivalent to 1 nautical mile. The distance represented by a minute of longitude varies based on your latitude...the further north you are from the equator, 1 minute of longitude is equal to a lesser distance than closer to the equator. For the latitudes NJ spans, 1 minute of longitude is less than 1 nautical mile. Minutes are sometimes followed by the single quote (') notation. (39 30')
ss - seconds, a way to divide minutes into 60 increments. Seconds are sometimes followed by the double quote (") notation. (74 07' 30")
[ 05-24-2005, 05:16 PM: Message edited by: captadamnj ]
