gpsprof - profile a GPS and gpsd, plotting latency information
gpsprof [-?] [--debug LVL] [--device DEV] [--dumpfile FILE] [--formatter TYPE] [--help] [--host HOST] [--logfile FILE] [--port PORT] [--redo] [--subtitle SUBTITLE] [--terminal TERMINAL] [--threshold THRESHOLD] [--title TITLE] [--wait SECONDS] [--version] [-D LVL] [-d FILE] [-f TYPE] [-h] [-l FILE] [-m THRESHOLD] [-n SECONDS] [-r] [-S SUBTITLE] [-T TERMINAL] [-t TITLE] [-V] [[server[:port[:device]]]]
gpsprof performs accuracy, latency, skyview, and time drift profiling on a GPS. It emits to standard output a GNUPLOT program that draws one of several illustrative graphs. It can also be told to emit the raw profile data.
Information from the default spatial plot it provides can be useful for characterizing position accuracy of a GPS.
gpsprof uses instrumentation built into gpsd. It can read data from a local or remote running gpsd. Or it can read data from a saved logfile.
gpsprof is designed to be lightweight and use minimal host resources. No graphics subsystem needs to be installed on the host running gpsprof. Simply copy the resultant plot file to another host to be rendered with gnuplot.
The -f, --formatter option sets the plot type. Currently the following plot types are defined:
For purposes of the description, below, start-of-reporting-cycle (SORC) is when a device's reporting cycle begins. This time is detected by watching to see when data availability follows a long enough amount of quiet time that we can be sure we've seen the gap at the end of the sensor's previous report-transmission cycle. Detecting this gap requires a device running at 9600bps or faster.
Similarly, EORC is end-of-reporting-cycle; when the daemon has seen the last sentence it needs in the reporting cycle and ready to ship a fix to the client.
The components of the instrumented plot are as follows:
Because of RS232 buffering effects, the profiler sometimes generates reports of ridiculously high latencies right at the beginning of a session. The -m option lets you set a latency threshold, in multiples of the cycle time, above which reports are discarded.
-?, -h, --help
-d FILE, --dumpfile FILE
-d LVL, --debug LVL
-l FILE, --logfile FILE
-n SEC, --wait SEC
-S STR, --subtitle STR
-t STR, --title STR
-T TERM, --terminal TERM
Different installations of gnuplot will support different terminal types. Different terminal types may work better for you than other ones. "-T png" will generate PNG images. Use "-T jpeg" to generate JPEG images. "-T pngcairo" often works best, but is not supported by some distributions. The same terminal type may work very differently on different distributions.
To see which terminal types your copy of gnuplot supports:
gnuplot -e "set terminal"
Sending SIGUSR1 to a running instance causes it to write a completion message to standard error and resume processing. The first number in the startup message is the process ID to signal.
To display the graph, use gnuplot(1). Thus, for example, to display the default spatial scatter plot, do this:
gpsprof | gnuplot -persist
To generate an image file:
gpsprof -T png | gnuplot > image.png
To generate a polar plot, and save the GPS data for further plots:
gpsprof -f polar -T jpeg -l polar.json | gnuplot > polar.png
Then to make the matching polarused and polarunused plots and pngs from the just saved the GPS data:
gpsprof -f polarused -T jpeg -r < polar.json > polarused.plot gnuplot < polarused.plot > polarused.png gpsprof -f polarunused -T jpeg -r < polar.json > polarunused.plot gnuplot < polarunused.plot > polarunused.png
Eric S. Raymond <firstname.lastname@example.org>.
|6 December 2020||The GPSD Project|