$ gpspipe -w # log to stdout
$ gpspipe -w -o abc.log # log to a file
To auto-log on startup, insert the following line to the file /etc/rc.local:
gpspipe -wdl -o /PATH/TO/DIRECTORY/`shuf -i 100000000-999999999 -n 1`.log
According to the
manpage, the
option -d causes it to run as a daemon, -l to sleep for ten seconds before
attempting to connect to gpsd (useful when running as a daemon, giving gpsd time
to start before attempting a connection).
shuf -i 100000000-999999999 -n 1 gives a random filename, so log files would
not be accidentally overwritten. Using date/time as filename in this case is not
ideal, because system time may not have been synced during such an early stage.
We are after lines such as this:
{"class":"TPV","device":"/dev/ttyACM0","mode":2,"time":"2018-06-26T06:20:02.009Z","ept":0.003,"lat":10.23456789,"lon":100.23456789,"track":200.3456,"speed":0.235,"eps":11.22}
TPV is the keyword. But there are also lines such as this, without lat/lon,
which we want to avoid:
{"class":"TPV","device":"/dev/ttyACM0","mode":1}
To get the first line with lat/lon:
$ grep TPV xxxxx.log | grep -m 1 lat
To get the last line with lat/lon:
$ grep TPV xxxxx.log | grep lat | tail -n 1
To count the number of lat/lon available:
$ grep TPV xxxxx.log | grep lat | wc -l
To extract all lat/lon, along with their times (you may have to install the
command-line JSON parser beforehand: sudo apt-get install jq):
$ grep TPV xxxxx.log | grep lat | jq -r '"\(.lat), \(.lon), \(.time)"'
If GPS signal is very good, you may notice two lat/lon per second. In many cases, you may not even need one per second. For example, you can keep one for every two lines, or three lines:
$ grep TPV xxxxx.log | grep lat | sed -n '1~2p' | jq -r '"\(.lat), \(.lon), \(.time)"'
$ grep TPV xxxxx.log | grep lat | sed -n '1~3p' | jq -r '"\(.lat), \(.lon), \(.time)"'
Use sed -n '/pattern/,/pattern/p' to select a time range. For example, to
extract only those between 14:30:00 and 15:00:00:
$ grep TPV xxxxx.log \
| grep lat \
| sed -n '/14:30:00/,/15:00:00/p' \
| sed -n '1~2p' \
| jq -r '"\(.lat), \(.lon), \(.time)"'
After you are happy with the extractions, you can plot them using the following websites:
https://www.darrinward.com/lat-long/
Assuming good GPS signals, one hour can produce 5 MB of logs. That is, 200 hours can produce 1 GB. Clean them periodically, or consider using logrotate.