The first step is to check the navigation in the GPS files. One file - L5F2 - had a sizeable navigation gap of approximately 6 minutes. This file was split into 2 parts effectively eliminating the navigation gap. The resulting new files are L5F2_part1 and L5F2_part2. Both the GPS files and the STG files were split into the new parts. Additionally the navigation in the GPS files were inspected visually. This was done by quickly parsing the GPS text files into comma-delimited text files with a header line, and then viewing the files in ArcMap 9.2. The AWK script used to parse the navigation was awkhold.
awkhold:
awkhold:
BEGIN {
FS = ","
}
{
FS = ","
ARGC = 2
depth = -9999
temp = -9999
if ($1=="$GPRMC")
{
utctime = $2
utcdate = $10
latdeg = substr($4,1,2)
latmin = substr($4,3,6)
declat = latdeg + (latmin/60)
londeg = substr($6,1,3)
lonmin = substr($6,4,6)
declon = -1 * (londeg + (lonmin/60))
if (NR==1) {
holddepth = -9999
holdtemp = -9999
}
else {
printf("%s, %s, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, holdutcdate, holddeclon, holddeclat, holddepth, holdtemp, ARGV[2])
}
holdutctime = utctime
holdutcdate = utcdate
holddeclon = declon
holddeclat = declat
holddepth = -9999
holdtemp = -9999
}
if ($1=="$SDDPT")
{
depthreal = $2
holddepth = depthreal
}
if ($1=="$SDMTW")
{
tempreal = $2
holdtemp = tempreal
}
}
END {
printf("%s, %s, %9.6f, %9.6f, %5.1f, %5.1f, %s\n", holdutctime, holdutcdate, holddeclon, holddeclat, holddepth, holdtemp, ARGV[2])
}
This file was executed by a shell script to effectively batch process all the files in a single folder with the extension gps. The batch processor was dohold.
dohold:
files=`ls *.gps | cut -d. -f1 | tr "[A-Z"] ["a-z"]`
for file in $files
do
awk -f awkhold $file.gps $file > $file.holds
done
Under Cygwin, all of the *.holds files were concatenated into a single comma-delimited text file and a header line added to the file. The header line added to the text file was: gpstime, gpsdate, longitude, latitude, depth_m, temp_c, line.
Using ArcMap 9.2 - Tools - Add XY Data, the comma-delimited text file was added as an event theme to ArcMap. No erroneous points were detected.