View Full Version : newbie GPS question

01-08-2014, 00:43
The GPS on my car gives the coordinates in degrees minutes and seconds (e.g., 33 48 15). My handheld unit gives the digital version. If I were to convert the the above coordinates to digital would that be 33 48.25?

01-08-2014, 09:12
yes - 1 minute = 60 seconds, so 15 seconds is equal to a quarter (0.25) of a minute.

If you do a lot of coordinate conversion, the US Army Geospatial Center has a coordinate conversion program called Corpscon available free at http://www.agc.army.mil/Missions/Corpscon.aspx

01-08-2014, 09:25
In my limited experience, it's easy enough to change the format of any GPS device's read-out. In your case, your car is reading in DD MM SS (degrees:minutes:seconds), and your handheld is in DD MM.MM (degrees:decimal minutes). Play around with the menu. Several other formats are available, as well as UTM and various other coordinate systems. Though you got it right, there's no need for mental conversions.

01-08-2014, 10:08
Always frustrating with all the different coordinate systems on GPSs. I was very reluctant at first, but finally I saw the light and started using UTM coordinates. Out in the field it helps to know how many meters north/south and east/west you are from a particular waypoint, for example. Its frustrating to try to convert minutes and seconds into distances! There are good rules of thumb, like a minute is about 3/4 mile (I think), so a second is roughly 75 feet (at mid-USA latitudes), something like that, for example, but with UTM coordinates, its a no-brainer, as long as you can think in meters (3.3 feet per meter). Try UTM sometime. Trouble is, a lot of printed maps use D/M/S and all the variants thereof.

01-08-2014, 10:09
Use of a single format across units is the best solution. The best way to avoid a conversion error is not to do the conversion! We've standardized our field crews on a decimal degree format (DD.DDD) for the handheld units used to locate established points in the field. It's cut down on a lot of transcription and conversion errors. We still use state plane coordinates for the survey-grade units but these are generally not available on recreational-grade handheld units.

You should also ensure that all of your GPS devices are using the same datum. The common ones are WGS84, NAD27, and NAD83. Not to get too far into the weeds here, but a datum is a means of describing the shape of the earth. Even though the coordinates may be the same numerically, there will be differences in the physical location of a measured point if different datums are used. Granted, the differences may be of no practical consequence for hiking given the use of the data and the inherent measurement uncertainty in a handheld GPS, but its good practice to use a common datum to compare measured points.

01-08-2014, 10:13
Switch from DMS to DDD, if you lost the directions you can google "Switching Garmin Model xxx from DMS to DDD.

01-09-2014, 13:37
Thanks to everyone for the input. Y'all have been very helpful.