gpsd/man/gpsprof.xml

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<!DOCTYPE refentry PUBLIC
   "-//OASIS//DTD DocBook XML V4.1.2//EN"
   "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
<refentry id='gpsprof.1'>
<refentryinfo><date>30 March 2020</date></refentryinfo>
<refmeta>
<refentrytitle>gpsprof</refentrytitle>
<manvolnum>1</manvolnum>
<refmiscinfo class="source">The GPSD Project</refmiscinfo>
<refmiscinfo class="manual">GPSD Documentation</refmiscinfo>
</refmeta>
<refnamediv id='name'>
<refname>gpsprof</refname>
<refpurpose>profile a GPS and gpsd, plotting latency information</refpurpose>
</refnamediv>
<refsynopsisdiv id='synopsis'>

<cmdsynopsis>
  <command>gpsprof</command>
      <arg choice='opt'>-D <replaceable>debuglevel</replaceable></arg>
      <arg choice='opt'>-d <replaceable>dumpfile</replaceable></arg>
      <arg choice='opt'>-f <replaceable>plot_type</replaceable></arg>
      <arg choice='opt'>-h </arg>
      <arg choice='opt'>-l <replaceable>logfile</replaceable></arg>
      <arg choice='opt'>-m <replaceable>threshold</replaceable></arg>
      <arg choice='opt'>-n <replaceable>samplecount</replaceable></arg>
      <arg choice='opt'>-r </arg>
      <arg choice='opt'>-S <replaceable>subtitle</replaceable></arg>
      <arg choice='opt'>-T <replaceable>terminal</replaceable></arg>
      <arg choice='opt'>-t <replaceable>title</replaceable></arg>
      <arg choice='opt'>[server[:port[:device]]]</arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1 id='description'><title>DESCRIPTION</title>

<para><application>gpsprof</application> 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.</para>

<para>Information from the default spatial plot it provides can be
useful for characterizing position accuracy of a GPS.</para>

<para><application>gpsprof</application> uses instrumentation built
into <application>gpsd</application>.  It can read data from a local
or remote running <application>gpsd</application>.  Or it can read
data from a saved logfile.</para>

<para><application>gpsprof</application> is designed to be lightweight
and use minimal host resources.  No graphics subsystem needs to be
installed on the host running <application>gpsprof</application>.  Simply
copy the resultant plot file to another host to be rendered
with <application>gnuplot</application>.
</para>

</refsect1>
<refsect1 id='options'><title>OPTIONS</title>

<para>The -f option sets the plot type.  Currently the following plot
types are defined:</para>

<variablelist>
<varlistentry>
<term>space</term>
<listitem>
<para>Generate a scatterplot of fixes and plot probable error circles.
This data is only meaningful if the GPS is held stationary while
<application>gpsprof</application> is running.  Various statistics about
the fixes are listed at the bottom.  This is the default plot type.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>polar</term>
<listitem>
<para>Generate a heat map of reported satellite Signal to Noise Ratio
(SNR) using polar coordinates.  A colored dot is plotted for
each satellite seen by the GPS.  The color of dot corresponds to the
SNR of the satellite.  The dots are plotted by azimuth and
elevation.  North, azimuth 0 degrees, is at the top of the plot.
Directly overhead, elevation of 90 degrees, is plotted at the center.
Useful for analyzing the quality of the skyview as seen by the GPS.
</para>
</listitem>
</varlistentry>

<varlistentry>
<term>polarunused</term>
<listitem>
<para>Similar to the polar plot, but only unused satellites
are plotted.  Useful for seeing which parts of the antenna skyview
are obstructed, degraded, below the GPS elevation mask, or otherwise
rejected.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>polarused</term>
<listitem>
<para>Similar to the polar plot, but only satellites used to compute
fixes are plotted.  Useful for seeing which parts of the antenna
skyview are being used in fixes.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>time</term>
<listitem>
<para>Plot delta of system clock (NTP corrected time) against GPS time
as reported in PPS messages.  The X axis is sample time in seconds
from the start of the plot.  The Y axis is the system clock delta from
GPS time.</para>
</listitem>
</varlistentry>

<varlistentry>
<term>instrumented</term>
<listitem>
<para>Plot instrumented profile.  Plots various components of the total
latency between the GPS's fix time and when the client receives the
fix.</para>
<para>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.</para>

<para>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.</para>

<para>The components of the instrumented plot are as follows:</para>

<variablelist>
<varlistentry>
<term>Fix latency</term>
<listitem>
<para>Delta between GPS time and SORC.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>RS232 time</term>
<listitem>
<para>RS232 transmission time for data shipped during the cycle
(computed from character volume and baud rate).</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Analysis time</term>
<listitem>
<para>EORC, minus SORC, minus RS232 time.  The amount of real time the daemon
spent on computation rather than I/O.</para>
</listitem>
</varlistentry>
<varlistentry>
<term>Reception time</term>
<listitem>
<para>Shipping time from
the daemon to when it was received by <application>gpsprof</application>.</para>
</listitem>
</varlistentry>
</variablelist>

<para>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.</para>

</listitem>
</varlistentry>
<varlistentry>
<term>uninstrumented</term>
<listitem>
<para>Plot total latency without instrumentation.  Useful mainly as a
check that the instrumentation is not producing significant distortion.
The X axis is sample time in seconds from the start of the plot.  The Y
axis is latency in seconds.  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.</para>
</listitem>
</varlistentry>
</variablelist>


<para>The -d option dumps the plot data, without attached gnuplot
code, to a specified file for post-analysis.</para>

<para>The -D sets debug level.</para>

<para>The -h option makes <application>gpsprof</application> print
a usage message and exit.</para>

<para>The -l option dumps the raw JSON reports collected from the device
to a specified file.</para>

<para>The -n option sets the number of packets to sample.  The default
is 100.  Most GPS are configured to emit one fix per second, so 100
samples would then span 100 seconds.</para>

<para>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.</para>

<para>The -S option sets a text string to be included in the plot
as a subtitle.  This will be below the title.</para>

<para>The -t option sets a text string to be the plot title.  This
will replace the default title.</para>

<para>The -T option generates a terminal type setting into the gnuplot
code.  Typical usage is "-T png", or "-T pngcairo" telling gnuplot to
write a PNG file.  Without this option gnuplot will call its X11 display
code.</para>
<para> Different installations of <application>gnuplot</application> 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.</para>

</refsect1>
<refsect1 id='signals'><title>SIGNALS</title>
<para>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.</para>
</refsect1>

<refsect1 id='examples'><title>EXAMPLES</title>
<para>To display the graph, use
<citerefentry><refentrytitle>gnuplot</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
Thus, for example, to display the default spatial scatter plot, do
this:

<programlisting>
gpsprof | gnuplot -persist
</programlisting>
</para>

<para>To generate an image file:

<programlisting>
gpsprof -T png | gnuplot &gt; image.png
</programlisting>
</para>
<para>
To generate a polar plot, and save the GPS data for further plots:
<programlisting>
gpsprof -f polar -T jpeg -l polar.json | gnuplot &gt; polar.png
</programlisting>
Then to make the matching polarused and polarunused plots and pngs from
the just saved the GPS data:
<programlisting>
gpsprof -f polarused -T jpeg -r &lt; polar.json &gt; polarused.plot
gnuplot &lt; polarused.plot &gt; polarused.png
gpsprof -f polarunused -T jpeg -r &lt; polar.json &gt; polarunused.plot
gnuplot &lt; polarunused.plot  &gt; polarunused.png
</programlisting>
</para>

</refsect1>
<refsect1 id='see_also'><title>SEE ALSO</title>
<para>
<citerefentry><refentrytitle>gpsd</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gps</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>libgps</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>libgpsmm</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsfake</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpsctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gpscat</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>gnuplot</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
</refsect1>

<refsect1 id='maintainer'><title>AUTHOR</title>

<para>Eric S. Raymond <email>esr@thyrsus.com</email>.</para>

</refsect1>

</refentry>