That depends on the version of the tools:
hcxdumptool >= v 6 require hcxpcapngtool --nmea to convert the NMEA sentences or hcxpcaptool --nmea. I dropped that xml conversion (and gpsd), because GPSBabel can do this much better.
hcxpcaptool -g uses old format from old hcxdumptool
hcxpcaptool ----nmea=<file> uses new format from latest hcxdumptool
format: NMEA 0183 $GPGGA, $GPRMC, $GPWPL
hcxpcapngtool --nmea=<file> uses new format from latest hcxdumptool
output GPS data in NMEA format
format: NMEA 0183 $GPGGA, $GPRMC, $GPWPL
BTW:
I pushed a fix for (old) hcxpcaptool. Now we have two internal counters: one for GPSD old JSON format and one for NME sentences.
JSON format produce too much overhead and that is the reason for me, to drop it.
If you run
case 1:
$ hcxdumptool --use_gps_device=your_device
NMEA sentences should be written directly to the pcpang file (custom comment field)
additional you can use --nmea=your_nmea_file to save them separate to a file (on the fly)
case 2:
To retrieve the NMEA data from the pcapng file (case 2), run:
$ hcxpcapngtool --nmea=converted_nmea_sentences_from_pcapng_file
Then use GPSbabel to convert them for use with Viking (case 2):
$ gpsbabel -i converted_nmea_sentences_from_pcapng_file -f hcxdumptool.nmea -o gpx -F file.gpx
or (case 1)
$ gpsbabel -i your_nmea_file -f hcxdumptool.nmea -o gpx -F file.gpx
gpsbabel offers hundreds of options to convert the NMEA sentences to whatever you want. See gpsbabel -h
A GUI is available, too:
https://www.gpsbabel.org/screenshots.html