Provided by: gpsd-clients_2.30-1ubuntu3_i386 bug

NAME

       gpsprof - profile a GPS and gpsd, plotting latency information

SYNOPSIS

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

DESCRIPTION

       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

OPTIONS

       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:

       space  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.

       uninstrumented
              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.

       raw    Plot raw data.

       split  Each sentence has its RS232 latency time colored differently.

       cycle  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 plots conveys the following information:

       RS232 time
              Minimum time required to send the sentence from the GPS to gpsd.
              This is computed, not measured, and may be an underestimate.

       Other line latency
              The transmission latency between the GPS and gpsd not  accounted
              for  by  RS232 time. Total line latency (the sum of this bar and
              RS232 time) is measured;  it  begins  with  the  GPS  sentence’s
              timestamp  and  ends  with  a  timestamp  that gpsd generates at
              sentence-reading time, before it is decoded.

       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 (SiRF-II supports 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.

BUGS AND LIMITAIONS

       Probably  overestimates  TCP/IP  latency somewhat, as that includes the
       Python interpreter’s decode time. A C client would be faster.

SEE ALSO

        gpsd(8), xgps(1), libgps(3), libgpsd(3), gnuplot(1).

AUTHOR

       Eric S. Raymond <esr@thyrsus.com>. There is a  project  page  for  gpsd
       here: http://gpsd.berlios.de/.

                                                                    GPSPROF(1)