Raw navigation data were saved in ASCII text format. Original navigation file name convention is JDXXX_A.txt, where JD is the Julian day, XXX is the numeric Julian day, and _A indicated that this is a temporary file. The reformatted log files are named JDXXX.txt. No editing was done in the reformatting, just a rearrangement of records into files organized by Julian day. However, included in the zip file of data is an AWK script (awkseth.gpgga10005.sda.awk) that can be used to extract the navigation from each log file into the following format: time, latitude (in decimal degrees), longitude (in decimal degrees), Julian day, source file.
$GPGGA is GPS fix data in the format "$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.
Example: $GPGGA,173356.00,4204.848996,N,07036.929067,W,4,09,01.1,00003.278,M,-028.888,M,01,0000*56 UTC Time = 173356 Latitude = 4204.848996 N Longitude = 7036.929067 W Fix Quality = 4 Number of satellites = 9 HDOP = 01.1 relative accuracy of horizontal position Altitude = 3.278 meters above mean sea level Height of geoid above WGS84 ellipsoid = -28.888 meters Time since last update = 01 Checksum = *57.
$GPVTG is track made good and ground speed in the format "$GPCTG, true, T, mag, M, grsp1, N, grsp2, K, mode", where true=true course made good over ground in degrees, T= True, mag=magnetic course made good over ground in degrees, M=magnetic, grsp1=ground speed, N=Knots, grsp2=ground speed, K=Kilometers per hour, mode=Mode indicator (A=Autonomous, D=Differential, E=Estimated, N=Data not valid).
Example: $GPVTG,340.39,T,356.37,M,005.50,N,010.18,K,D*27 True course made good: 340.39 Magnetic course made good: 356.37 Ground speed (knots) = 5.5 Ground speed (kilometers) = 10.18 Mode=Differential