Hello world 🙂 Welcome to my blog on GPS data. When we connect a GPS transceiver to our computer we get some data in a standard format which is called NMEA sentence, NMEA stands for National Marine Electronics Association. Each sentence begins with a ‘$’ and ends with a carriage return/line feed sequence and can be no longer than 80 characters of visible text. The data is contained within this single line with data items separated by commas. The data itself is just ASCII text and may extend over multiple sentences in certain specialized instances but is normally fully contained in one variable length sentence.

Hardware Connection:
The Hardware interface for GPS module is designed to meet NMEA requirements. They are compatible with the serial RS232 ports however NMEA recommends EIA-422 protocol. The interface can be set to 9600 baud, 8 bit data, no parity, and hardware mode off.
Now at 9600bps you can only send 960 characters in one second so NMEA sentences can be extended to 6 different sentences.
Some of the conman NMEA sentences.

GPGGA : Fix data
GPGLL : LAT/LON data
GPGSA : overall satellite reception data
GPGSV : detailed satellite data
GPVTG : vector track and speed over ground

  • GPGGA – data which provides accurate 3-Dimentional location and accurate data. provdes latitude longitude UTC time height above the sea level.
$GPGGA,123519,4807.038,N,01131.000,E,1,08,0.9,545.4,M,46.9,M,,*47
Where:
     GGA          Global Positioning System Fix Data
     123519       Fix taken at 12:35:19 UTC
     4807.038,N   Latitude 48 deg 07.038' N
     01131.000,E  Longitude 11 deg 31.000' E
     1            Fix quality: 0 = invalid
                               1 = GPS fix (SPS)
                               2 = DGPS fix
                               3 = PPS fix
			       4 = Real Time Kinematic
			       5 = Float RTK
                               6 = estimated (dead reckoning) (2.3 feature)
			       7 = Manual input mode
			       8 = Simulation mode
     08           Number of satellites being tracked
     0.9          Horizontal dilution of position
     545.4,M      Altitude, Meters, above mean sea level
     46.9,M       Height of geoid (mean sea level) above WGS84
                      ellipsoid
     (empty field) time in seconds since last DGPS update
     (empty field) DGPS station ID number
     *47          the checksum data, always begins with *</pre>
<pre>
  • GPGLL – provides geographical latitudes and longitudes
  $GPGLL,4916.45,N,12311.12,W,225444,A,*1D

Where:
     GLL          Geographic position, Latitude and Longitude
     4916.46,N    Latitude 49 deg. 16.45 min. North
     12311.12,W   Longitude 123 deg. 11.12 min. West
     225444       Fix taken at 22:54:44 UTC
     A            Data Active or V (void)
     *iD          checksum data

  • GPGSA – provides the detailed nature and fixes of the satellite with the horizontal and vertical dillution.
 $GPGSA,A,3,04,05,,09,12,,,24,,,,,2.5,1.3,2.1*39

Where:
 GSA Satellite status
 A Auto selection of 2D or 3D fix (M = manual)
 3 3D fix - values include: 1 = no fix
 2 = 2D fix
 3 = 3D fix
 04,05... PRNs of satellites used for fix (space for 12)
 2.5 PDOP (dilution of precision)
 1.3 Horizontal dilution of precision (HDOP)
 2.1 Vertical dilution of precision (VDOP)
 *39 the checksum data, always begins with *
  • GPGSV – provides the details of satellites in view along with the elevation and azimuth angles in degrees and signal to noise ratio for each satellite.
 $GPGSV,2,1,08,01,40,083,46,02,17,308,41,12,07,344,39,14,22,228,45*75

Where:
 GSV Satellites in view
 2 Number of sentences for full data
 1 sentence 1 of 2
 08 Number of satellites in view

 01 Satellite PRN number
 40 Elevation, degrees
 083 Azimuth, degrees
 46 SNR - higher is better
 for up to 4 satellites per sentence
 *75 the checksum data, always begins with *
  • GPVTG – its for the velocity mode and used in the track mode to get the speed over ground and the orientation
$GPVTG,054.7,T,034.4,M,005.5,N,010.2,K*48

where:
 VTG Track made good and ground speed
 054.7,T True track made good (degrees)
 034.4,M Magnetic track made good
 005.5,N Ground speed, knots
 010.2,K Ground speed, Kilometers per hour
 *48 Checksum

You will receive the above NMEA format while tracking from a GPS transreciever which can be used for geopositioning in your applications.
Happy Tracking 🙂