Please Sign In


New To Sportsman Network?
  • GPS Formats ?

    Reply
     
    Sir,
    I have a Garmin GPS/Plotter that gives m Lon/Lat in a (7) seven digit readout, example: 35.26.804N 077.06.099W.

    I ahve a PDA with Maptech software, it too gives me seven digit readout but the decimal point is not shown, example: N35 26'48.26' W78 06'6.53'.
    Can you please explain what format this is and can I convert this format to the Garmin.

    Thank you
    Bill Acree
    Reply
    Different Position Formats
    ~ Captain Paul’s Response to Bill Acree ~
    The Garmin position format is configured to read degrees, minutes and thousandths of minutes. (DDD,MM.mmm) Using this format is generally the most accurate way to represent a position using a consumer type GPS receiver.

    a change in the last position after the decimal point of one integer (.001 to .002) amounts to a position change of 6.076 feet.

    At this latitude, one minute of a degree of llatitude equals one nautical mile or 6076.115 feet. Therefore, one tenth of a nautical mile (.m) equals 607.612 feet, one hundredth of a nautical mile (.mm) equals 60.7612 feet and one thousandth of a nautical mile (.mmm) equals 6.076 feet.

    In the DD,MM,SS.S format, one digit difference in the place after the decimal (00.1”) equals about 10.1 feet of latitude. The DD,MM.MMM is a more precise way to state a position than DD,MM,SS.S.

    The position you describe as showing in your PDA loaded with Maptech mapping software, appears to be shown in degrees, minutes, seconds and hundredths of seconds (DDD,MM,SS.ss)
    The position should actually shown as N 35* 26’ 48.26”, etc.

    There are three ways to have both units “speaking” in the position format language. Either change the Position Format setting in the Garmin or preferably change the Maptech software to display the positions in the same format as the Garmin unit.

    For Maptech Offshore Navigator including Digital Chartkit,
    Click on “View” in the top tool bar, then click on “Options.”
    Once the window appears, find the LAT/Long format box and select the DDD,MM.mmm format from the drop down box that will appear when you click on the arrow.

    If you are operating the Maptech TERRAIN Navigator software, click on “File,” then “Preferences,” then “General.” When the drop down General window appears, select the “Coordinates arrow and change the format to D,M.M. This setting will display the PDA positions in the same format as the Garmin.

    Now that we discussed two ways, you can use the third, although it will require a little math on your part. The third way is to manually convert either position to the other.

    To convert seconds and tenths of seconds (SS.S”) to thousandths of a minute, divide by 60. (30 seconds divided by 60 = .500 minutes)

    To convert thousandths of a minute (.MMM’) to seconds SS.S”), multiply the thousandths of minutes by 60. (.210’{minutes} x 60 = 12 .6” {seconds}).

    ~ Remember that almost as important as the position format, is the DATUM that was used to obtain the position. The difference between NAD 27 and WGS 84 could result in a shift in the physical position as much as 400 feet

    When obtaining and entering a position that you may want locate, plot to or from a map, you should determine what DATUM was used to obtain the position and convert it to the datum used by the map. The coordinates (waypoints) should be entered using that DATUM.~ Entering a position that was obtained using one datum as a position in another datum can cause another error in position. I have seen a position error of over 1200 feet caused by using the wrong datum.

    So, be sure that the DATUM in both units are in the same format.
    ~ Captain Paul ~
    Reply