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GPSPROF(1) | GPSD Documentation | GPSPROF(1) |
NAME¶
gpsprof - profile a GPS and gpsd, plotting latency informationSYNOPSIS¶
gpsprof
[-f plot_type] [-m threshold]
[-n packetcount] [-t title] [-T terminal]
[-d dumpfile] [-l logfile] [-r]
[-D debuglevel] [-h] [[server[:port[:device]]]]
DESCRIPTION¶
gpsprof performs accuracy and latency profiling on a GPS. 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
gpsprof -T png | gnuplot >image.png
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: spaceGenerate 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 reports that contain fixes; staircase-like
artifacts in the plot are created when elapsed time from reports without fixes
is lumped in.
instrumented
Plot instrumented profile. Plots various
components of the total latency between the GPS's fix time fix and when the
client receives the fix.
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:
Fix latency
Delta between GPS time and SORC.
RS232 time
RS232 transmission time for data shipped
during the cycle (computed from character volume and baud rate).
Analysis time
EORC, minus SORC, minus RS232 time. The amount
of real time the daemon spent on computation rather than I/O.
Reception time
Shipping time from the daemon to when it was
received by gpsprof.
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 -t option sets a text string to be included in the plot title.
The -T option generates a terminal type setting into the gnuplot code. Typical
usage is "-T png" telling gnuplot to write a PNG file. Without this
option gnuplot will call its X11 display code.
The -d option dumps the plot data, without attached gnuplot code, to a specified
file for post-analysis.
The -l option dumps the raw JSON reports collected from the device to a
specified file.
The -r option replots from a JSON logfile (such as -l produces) on standard
input. Both -n and -l options are ignored when this one is selected.
The -h option makes gpsprof print a usage message and exit.
The -D sets debug level.
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.
SEE ALSO¶
AUTHOR¶
Eric S. Raymond esr@thyrsus.com.10 Feb 2005 | The GPSD Project |