Entity_and_Attribute_Overview:
The 12 National Marine Electronics Association (NMEA) strings stored in the raw navigation files are described below. The CSV files only contain the GPRMC navigation string parsed from the raw navigation files for each Julian day. No editing has been conducted on these data. The times recorded in the navigation files are in UTC.
$GPRMC is the recommended minimum Global Positioning System (GPS) data. For example, "$GPRMC,172814,A,4221.9562,N,07055.2928,W,9.1,51.3,210812,15.7,W,D*18" where:
172814 = Fix taken at 17:28:14 UTC
A = Status (A = active, V = void)
4221.9562,N = Latitude 42 degrees 21.9562 minutes North
07055.2928,W = Longitude 070 degrees 55.2928 minutes West
9.1 = Speed over the ground in knots
51.3 = Track angle in degrees true
210812 = UTC date August 21, 2012
15.7,W = Magnetic variation in degrees with direction (Westerly or Easterly)
D = Mode indicator (A = Autonomous, D = Differential, E = Estimated, N = Data not valid)
*18 = Checksum data, always begins with *
$GPRMB is the recommended minimum navigation sentence. For example, "$GPRMB,A,0.66,L,003,004,4917.24,N,12309.57,W,001.3,052.5,000.5,V*20" where:
A = Data status (A = active, V = void)
0.66,L = Cross-track error in nautical miles (9.99 max), steer Left to correct (or R = right)
003 = Origin waypoint ID
004 = Destination waypoint ID
4917.24,N = Destination waypoint latitude 49 degrees 17.24 minutes North
12309.57,W = Destination waypoint longitude 123 degrees 09.57 minutes West
001.3 = Range to destination in nautical miles (999.9 max)
052.5 = True bearing to destination
000.5 = Velocity towards destination in knots
V = Arrival alarm (A = arrived, V = not arrived)
*20 = Checksum data
Note: The above example is from a different dataset. GPRMB strings were not transmitted during this survey and were therefore recorded as "$GPRMB,A,,,,,,,,,,,,V,D*19" in the raw navigation files.
$GPGGA is essential GPS fix data. For example, "$GPGGA,172814,4221.9562,N,07055.2928,W,2,10,0.8,18.9,M,-33.0,M,,*45" where:
172814 = Fix taken at 17:28:14 UTC
4221.9562,N = Latitude 42 degrees 21.9562 minutes North
07055.2928,W = Longitude 070 degrees 55.2928 minutes West
2 = Fix quality (0 = invalid, 1 = GPS fix, 2 = DGPS fix, 3 = Precise Positioning System [PPS] fix, 4 = Real Time Kinematic [RTK] fix, 5 = RTK float, 6 = estimated, 7 = manual input mode, 8 = simulation mode)
10 = Number of satellites being tracked
0.8 = Horizontal dilution of position
18.9,M = Altitude above mean sea level (geoid), meters
-33.0,M = Height of geoid above WGS 84 ellipsoid, meters
[Empty field] = Time in seconds since last DGPS update
[Empty field] = DGPS station ID number
*45 = Checksum data
$GPGSA is overall satellite data. For example, "$GPGSA,A,3,01,03,06,07,08,11,13,17,19,,28,,0.0,0.8,0.8*3F" where:
A = Auto selection of 2D or 3D fix (M = manual)
3 = 3D fix (values include: 1 = no fix, 2 = 2D fix, 3 = 3D fix)
01,03,06,07,08,11,13,17,19,,28,, = Pseudo-Random Noise (PRN) number of satellites used for fix (space for 12)
0.0 = Position Dilution of Precision (PDOP)
0.8 = Horizontal Dilution of Precision (HDOP)
0.8 = Vertical Dilution of Precision (VDOP)
*3F = Checksum data
$GPGSV is data about the satellites in view. For example, "$GPGSV,3,1,12,01,41,157,48,03,21,059,48,06,08,058,33,07,64,197,45*7B" where:
3 = Number of sentences for full data
1 = Sentence 1 of 3
12 = Number of satellites in view
01 = Satellite PRN number
41 = Elevation in degrees
157 = Azimuth in degrees
48 = Signal-to-Noise Ratio (SNR; higher is better)
(The above four data fields may be repeated for up to four satellites per sentence. In the above example, they are repeated for four satellites.)
*7B = Checksum data
$GPGLL is geographic latitude and longitude data. For example, "$GPGLL,4221.9562,N,07055.2928,W,172814,A,D*52" where:
4221.9562,N = Latitude 42 degrees 21.9562 minutes North
07055.2928,W = Longitude 070 degrees 55.2928 minutes West
172814 = Fix taken at 17:28:14 UTC
A = Data status (A = active, V = void)
D = Mode indicator (A = Autonomous, D = Differential, E = Estimated, N = Data not valid)
*52 = Checksum data
$GPBOD is bearing origin to destination data. For example, "$GPBOD,045.,T,023.,M,DEST,START*01" where:
045.,T = Bearing 045 degrees True from "START" to "DEST"
023.,M = Bearing 023 degrees Magnetic from "START" to "DEST"
DEST = Destination waypoint ID
START = Origin waypoint ID
*01 = Checksum data
Note: The above example is from a different dataset. GPBOD strings were not transmitted during this survey and were therefore recorded as "$GPBOD,,T,,M,,*47" in the raw navigation files.
$GPVTG is velocity made good and ground speed data. For example, "$GPVTG,51.3,T,67.0,M,9.1,N,16.9,K,D*16" where:
51.3,T = True track made good in degrees
67.0,M = Magnetic track made good in degrees
9.1,N = Ground speed, knots
16.9,K = Ground speed, kilometers per hour
D = Mode indicator (A = Autonomous, D = Differential, E = Estimated, N = Data not valid)
*16 = Checksum data
$PGRME is a Garmin proprietary sentence about the estimated position error ("P" denotes proprietary, "GRM" is Garmin's manufacturer code, and “E” indicates the specific sentence type). For example, "$PGRME,2.5,M,3.1,M,4.0,M*2F" where:
2.5,M = Estimated Horizontal Position Error (HPE), meters
3.1,M = Estimated Vertical Position Error (VPE), meters
4.0,M = Overall spherical equivalent position error, meters
*2F = Checksum data
$PGRMZ is a Garmin proprietary sentence with altitude information ("P" denotes proprietary, "GRM" is Garmin's manufacturer code, and “Z” indicates the specific sentence type). For example, "$PGRMZ,55,f,*18" where:
55,f = Altitude, feet
[Empty field] = Position fix dimensions (2 = user altitude, 3 = GPS altitude)
*18 = Checksum data
Note: This sentence shows in feet, regardless of units shown on the display. For units with an altimeter, the altitude will be computed by the internal altimeter.
$PGRMM is a Garmin proprietary sentence about the map datum ("P" denotes proprietary, "GRM" is Garmin's manufacturer code, and “M” indicates the specific sentence type). For example, "$PGRMM,WGS 84*06" where:
WGS 84 = Currently active horizontal datum
*06 = Checksum data
$HCHDG is data about the magnetic heading, deviation, and variation. This string is used on Garmin eTrex Summit, Vista, and GPSMAP 76S receivers to output the value of the internal flux-gate compass. Only the magnetic heading and magnetic variation is shown in the message. For example, "$HCHDG,67.0,,,15.7,W*39" where:
67.0 = Heading
,, = Deviation (no data)
15.7,W = Variation and direction
*39 = Checksum data
$GPRTE is sent to indicate the names of the waypoints used in an active route. For example, "$GPRTE,1,1,c,*37" where:
1 = Total number of sentences for full data
1 = Sentence 1 of 1
c = Type (c = complete list of waypoints in this route, w = first listed waypoint is start of current leg)
[Empty field] = Route identifier
[Empty fields] = Waypoint identifiers (names)
*37 = Checksum data
Entity_and_Attribute_Detail_Citation:
