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       gpsprof - profile a GPS and gpsd, plotting latency information


       gpsprof [-f plot_type] [-m threshold] [-n packetcount] [-s speed]
               [-t title] [-h]


       gpsprof measures the various latencies between a GPS and its client. It
       emits to standard output a GNUPLOT program that draws an illustrative
       graph. It can also be told to emit the raw profile data. The
       information it provides can be useful for establishing an upper bound
       on latency, and thus on position accuracy of a GPS in motion.

       gpsprof uses instrumentation built into gpsd.

       To display the graph, use gnuplot(1). Thus, for example, to display the
       default spatial scatter plot, do this:

           gpsprof | gnuplot -persist


       The -f option sets the plot type. The X axis is samples (sentences with
       timestamps). The Y axis is normally latency in seconds. Currently the
       following plot types are defined:

           Generate a scattergram of fixes and plot a probable-error circle.
           This data is only meaningful if the GPS is held stationary while
           gpsprof is running. This is the default.

           Plot total latency without instrumentation. Useful mainly as a
           check that the instrumentation is not producing significant
           distortion. It only plots times for sentences that contain fixes;
           staircase-like artifacts in the plot are created when elapsed time
           from sentences without fixes is lumped in.

           Plot raw data.

           Each sentence has its RS232 latency time colored differently.

           Report on the set of sentences or packets emitted by the GPS, their
           send intervals, and the basic cycle time. (This report is plain
           text rather than a gnuplot script.)

       The instrumented time plot conveys the following information:

       RS232 time
           Time required to send the sentence from the GPS to gpsd. This
           measured from the time of the last zero-length read before the
           packet to when the packet sniffer recognizes a complete sentence,
           so there is a small aountt of computational overhead mixed in.

       Decode time
           Elapsed time between sentence reception and the moment that gpsd
           ships the resulting update to the profiling client.

       TCP/IP latency
           Elapsed time between the moment that gpsd ships the update to the
           profiling client and the moment it is decoded and timestamped.

       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.

       The -n option sets the number of packets to sample. The default is 100.

       The -s option sets the baud rate. Note, this will only work if the
       chipset accepts a speed-change command (SiRFstarII and SiRFstarIII
       support this feature).

       The -t option sets a text string to be included in the plot title.

       The -h option makes gpsprof print a usage message and exit.


       gpsd(8), gps(1), libgps(3), libgpsd(3), gpsfake(1), gpsctl(1),
       gpscat(1), gnuplot(1).


       Eric S. Raymond There is a project page for gpsd


        1. here