1GPSPROF(1)                    GPSD Documentation                    GPSPROF(1)
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NAME

6       gpsprof - profile a GPS and gpsd, plotting latency information
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SYNOPSIS

9       gpsprof [-f plot_type] [-m threshold] [-n packetcount] [-s speed]
10               [-t title] [-D debuglevel] [-h]
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DESCRIPTION

13       gpsprof measures the various latencies between a GPS and its client. It
14       emits to standard output a GNUPLOT program that draws an illustrative
15       graph. It can also be told to emit the raw profile data. The
16       information it provides can be useful for establishing an upper bound
17       on latency, and thus on position accuracy of a GPS in motion.
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19       gpsprof uses instrumentation built into gpsd.
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21       To display the graph, use gnuplot(1). Thus, for example, to display the
22       default spatial scatter plot, do this:
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24           gpsprof | gnuplot -persist
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OPTIONS

28       The -f option sets the plot type. The X axis is samples (sentences with
29       timestamps). The Y axis is normally latency in seconds. Currently the
30       following plot types are defined:
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32       space
33           Generate a scattergram of fixes and plot a probable-error circle.
34           This data is only meaningful if the GPS is held stationary while
35           gpsprof is running. This is the default.
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38       uninstrumented
39           Plot total latency without instrumentation. Useful mainly as a
40           check that the instrumentation is not producing significant
41           distortion. It only plots times for sentences that contain fixes;
42           staircase-like artifacts in the plot are created when elapsed time
43           from sentences without fixes is lumped in.
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45       raw
46           Plot raw data.
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48       split
49           Each sentence has its RS232 latency time colored differently.
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51       cycle
52           Report on the set of sentences or packets emitted by the GPS, their
53           send intervals, and the basic cycle time. (This report is plain
54           text rather than a gnuplot script.)
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56       The instrumented time plot conveys the following information:
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58       RS232 time
59           Time required to send the sentence from the GPS to gpsd. This
60           measured from the time of the last zero-length read before the
61           packet to when the packet sniffer recognizes a complete sentence,
62           so there is a small aountt of computational overhead mixed in.
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64       Decode time
65           Elapsed time between sentence reception and the moment that gpsd
66           ships the resulting update to the profiling client.
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68       TCP/IP latency
69           Elapsed time between the moment that gpsd ships the update to the
70           profiling client and the moment it is decoded and timestamped.
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72       Because of RS232 buffering effects, the profiler sometimes generates
73       reports of ridiculously high latencies right at the beginning of a
74       session. The -m option lets you set a latency threshold, in multiples
75       of the cycle time, above which reports are discarded.
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77       The -n option sets the number of packets to sample. The default is 100.
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79       The -s option sets the baud rate. Note, this will only work if the
80       chipset accepts a speed-change command (SiRFstarII and SiRFstarIII
81       support this feature).
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83       The -t option sets a text string to be included in the plot title.
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85       The -h option makes gpsprof print a usage message and exit.
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87       The -D sets debug level.
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SEE ALSO

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

94       Eric S. Raymond esr@thyrsus.com. There is a project page for gpsd
95       here[1].
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NOTES

98        1. here
99           http://gpsd.berlios.de/
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103The GPSD Project                  10 Feb 2005                       GPSPROF(1)