NMEA Transmitted Messages
The default communication parameters
for NMEA output are 4800 baud, 8 data bits, stop bit, and no parity.
Table
4-1 NMEA-0183 Output Messages
Global Positioning System Fix Data (GGA)
$GPGGA,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,M,<11>,<12>,<13><CR><LF>
1)
UTC time of position fix,
hhmmss.sss format
2)
Latitude, ddmm.mmmm format.
3)
Latitude hemisphere, N or S.
4)
Longitude, dddmm.mmmm format.
5)
Longitude hemisphere, E or W.
6)
Position Fix Indicator,
0 = fix not available, or invalid.
1 = GPS SPS Mode, fix valid.
2 = Differential GPS, SPS Mode, fix valid.
3 = GPS PPS Mode, fix valid.
7)
Number of sate1lites in use,
00 to 12.
8)
Horizontal Dilution of
Precision, 0.5 to 99.9.
9)
MSL Altitude, -9999.9 to
99999.9 meters.
10) Geoidal height, -999.9 to 9999.9 meters.
11) Differential GPS (RTCM SC-104) data age, number of seconds
since last valid RTCM transmission (nu1l if non-DGPS).
12) Differential Reference Station ID, 0000 to 1023. (null if
non-DGPS)
13) Checksum.
Geographic Position with
Latitude/Longitude
$GPGLL,<1>,<2>,<3>,<4>,<5>,<6>,<7><CR><LF>
1)
Latitude, ddmm.mmmm format.
2)
Latitude hemisphere, N or S.
3)
Longitude, dddmT1.mmmm
format.
4)
Longitude hemisphere, E or W.
5)
UTC time of position fix,
hhmmss format.
6)
Status, A = data valid or V =
data not valid.
7)
Checksum.
GNSS DOP and Active Satellites (GSA)
$GPGSA,<1>,<2>,<3>,<3>,,,,,<3>,<3>,<3>,<4>,<5>,<6>,<7><CR><LF>
1)
Mode 1, M = manual, A =
automatic.
2)
Mode 2, Fix type, 1 =not available,
2 = 2D, 3 = 3D.
3)
PRN number, 01 to 32, of
satellite used in solution, up to 12 transmitted.
4)
PDOP-Position dilu1ion of
precision, 0.5 to 99.9.
5)
HDOP-Horizontal dilution of
precision, 0.5 to 99.9.
6)
VDOP-Vertical di1ution of
precision, 0.5 to 99.9.
7)
Checksum.
GNSS Satellites in View (GSV)
$GPGSV,<1>,<2>,<3>,<4>,<5>,<6>,<7>,…<4>,<5>,<6>,<7>,<8><CR><LF>
1)
Total number of GSV sentences
to be transmitted, 0~3.
2)
Number of message, 0~3.
3)
Total number of satellites in
view, 00 to 12.
4)
Satellite PRN number, 01 to
32.
5)
Satellite elevation, 00 to 90
degrees.
6)
Satellite azimuth, 000 to 359
degrees, true.
7)
Signal to noise ratio (C/No)
00 to 99 dB, null when not tracking.
NOTE:
Items <4>,<5>,<6> and <7> repeat for each satellite in
view to a maximum of four (4) satellites per sentence. Additiona1 satellites in view information
must be sent in subsequent sentences. These fields will be null if unused.
8)
Checksum.
Recommended Minimum Specific GNSS Data
(RMC)
$GPRMC,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11><CR><LF>
1)
UTC time of position fix,
hhmmss.sss format.
2)
Status, A = data valid, V =
data not valid.
3)
Latitude, ddmm.mmmm format.
4)
Latitude hemisphere, N or S.
5)
Longitude, dddmmm.mmmm
format.
6)
Longitude hemisphere, E or W.
7)
Speed over ground, 0.0 to
1851.8 knots.
8)
Course over ground, 000.0 to
359.9 degrees, true.
9)
Date, ddmmyy format.
10) Magnetic variation, 000.0 to 180.O.
11) Degrees
12) Checksum.
Course Over Ground and Ground Speed
$GPVTG,<1>,T,<2>,M,<3>,N,<4>,K,<5><CR><LF>
1)
True course over ground, 000
to 359 degrees.
2)
Magnetic course over ground,
000 to 359 degrees.
3)
Speed over ground, 00.0 to
999.9 knots.
4)
Speed over ground, 00.0 to
1851.8 ko/hr.
5)
Checksum.
The
default extension for files used for
saving GPS strings are .csv, the standard extension for Microsoft Excel comma
delimited files. You can change this if you wish. The files can be edited in
any text editor or spreadsheet programme.
Sample GPS cature String
$GPGGA,145121.999,5121.2199,N,00032.5133,E,1,06,2.1,175.9,M,,,,0000*0A
Included with Xylon is a utility called OS Convert
which converts the GPS raw data to the UK Ordnance Survey co-ordinate system.
You can use this to convert data captured anywhere to real world co-ordinates
in metres for plotting etc. though you should check locally to see what corrections
should be applied. There are many utilities available on the internet to
convert NMEA strings to various national systems. Follow this link for a
listing of conversion information.