The times recorded in the navigation file are in UTC (Coordinate Universal Time). Keywords and the information they provide are as follows:
FTP: The first record located at the top of the header used to identify the file format.
VER: HYPACK version number.
INF: General survey information filled in by the data technician.
FIL: Raw format file.
ELL: Ellipsoid information. The name of the ellipsoid followed by the semi-major axis in meters and the flattening ration.
PRO: Project information record where TME indicates Transverse Mercator and the central meridian of -69 indicates UTM, zone 19.
DTM: Datum transformation record
GEO: Geoid model. Blank if not present.
HVU: Horizontal and Vertical Units (meters)
TND: Survey time and date in UTC.
DEV 0: Indicated that the lines collected with device designation 0 are lines of single-beam echo sounder.
OFF: device offsets (none used during this data collection)
DEV 1: Indicates that lines collected with device designation 1 are using Ashtech Z-Extreme, capable of recording antenna elevations above a vertical datum (i.e. real-time kinematic, RTK)
OFF: device offsets (non used during data collection)
LIN 2: planned line data follows
PTS: planned line waypoints (eastings and northings, UTM, zone 19N, meters)
LBP: planned line begin point (easting and northings, UTM zone 19N, meters)
LNN 1: planned line name
EOL: end of planned line
EOH: end of header
The remaining elements have similar information in the first 3 columns. The first column will indicate the data type, the second column will indicate the device that recorded the information (e.g. 1 for Ashtech receiver) and the third column is the time tag (seconds past midnight) that is also sometimes referred to as the latency. The remaining information on each line is specific to the data type.
MSG: Message string in the format "MSG dn t message" where dn=device number; t=time tag (seconds past midnight); message is the message sent from the device.
EC1: echo sounding (singe frequency). Format "EC1 dn t rd", where dn=device number, t=time tag (seconds past midnight), rd=raw depth.
POS: Position of the ship in the format "POS dn t x y" where dn=device number; t=time tag (seconds past midnight); x=easting; y=northing. On this cruise these values are in UTM, Zone 19, WGS84.
QUA: Position quality information in the format "QUA dn t n m h sat mode" where dn=device number; t=time tag (seconds past midnight); n=number of values to follow; m = 10 minus HDOP (horizontal dilution of precision); h=HDOP; sat=number of satellites; mode=GPS mode (NMEA 0183 standard values) where 0=fix not available or invalid; 1=GPS fix; 2=Differential GPS fix; 3=GPS PPS Mode fix; 4=RTK fix; 5=RTK float.
RAW: Position information in the format "RAW dn t n lat long alt utc" where dn=device number; t=time tag (seconds past midnight); n=number of values to follow; lat=raw latitude X 100; long=raw longitude X 100; alt=antenna altitude above ellipsoid (meters); utc=GPS time in the format HHMM.
TID: Tide correction. Format "dn t dc", where dn=device number, t=time tag (seconds past midnight), dc = draft correction.
FIX: Fix (event) mark. Format "FIX vn", where n=FIX format version number, Always 2nd record in file.
The (National Marine Electronics Association) NMEA strings $GPGGA, $GPVTG, and $GPZDA are stored in the HYPACK file. These are defined as follows.
$GPGGA is GPS fix data in the format "$GPGGA, t, lat, lath, long, longh, q, sat, h, a, M, alt, M, t2, refcheck" where t=time in UTC in the format hhmmss.ss; lat=latitude in the format ddmm.mmmmmm; lath= N or S indicating the latitude hemisphere; long=longitude in the format dddmm.mmmmmm; longh=E or W indicating the hemisphere; q=fix quality where 0=fix not available or invalid; 1=GPS fix; 2=Differential GPS fix; 3=GPS PPS Mode fix; 4=RTK fix; 5=RTK float; sat=number of satellites; h=Horizontal Dilution of Precision (HDOP); a=Antenna altitude above mean sea level (geoid); M= units of antenna altitude in meters; alt=height of geoid above WGS84 ellipsoid; M=units of geoidal height in meters; t2=time since last DGPS update; refcheck=DGPS reference station id and the checksum.
UTC Time = 163052
Latitude = 4118.964217 N
Longitude = 7036.966471 W
Fix Quality = 4
Number of satellites = 10
HDOP = 00.9 relative accuracy of horizontal position
Altitude = 5.332 meters above mean sea level
Height of geoid above WGS84 ellipsoid = -30.554 meters
Time since last update = 01
Checksum = *57.
$GPVTG is track made good and ground speed in the format "$GPCTG, true, T, mag, M, grsp, N, grdp, K, mode", where t=true course made good over ground in degrees, T= True, m=magnetic course made good over ground in degrees, M=magnetic, gdsp=ground speed, N=Knots, grsp=ground speed, K=Kilometers per hour, mode=Mode indicator (A=Autonomous, D=Differential, E=Estimated, N=Data not valid).
True course made good: 089.23
Magnetic course made good: 104.82
Ground speed (knots) = 4.86
Ground speed (kilometers) = 9.02
$GPZDA is UTC Date/Time and Local Time Zone Offset in the format "$GPZDA,hhmmss.ss,xx,xx,xxxx,xx,xx" where hhmmss.ss=UTC, xx=Day, 01 to 31, xx=month, 01 to 12, xxx=Year, xx=Local zone description, 00 to +/- 13 hours, xx=Local zone minutes description (same sign as hours), checksum.
UTC day = 09
UTC month = 08
UTM year = 2007
Local zone hours = null
Local zone minutes = null
Checksum = *60