gpsprof(1) GPSD Documentation gpsprof(1)
NAME
gpsprof - profile a GPS and gpsd, plotting latency information
SYNOPSIS
gpsprof [OPTIONS] [server[:port[:device]]]
gpsprof -h
gpsprof -V
DESCRIPTION
gpsprof 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.
Information from the default spatial plot it provides can be useful for
characterizing position accuracy of a GPS.
gpsprof uses instrumentation built into gpsd. It can read data from a
local or remote running gpsd. Or it can read data from a saved logfile.
gpsprof is designed to be lightweight and use minimal host resources. No
graphics subsystem needs to be installed on the host running gpsprof.
Simply copy the resultant plot file to another host to be rendered with
gnuplot(1).
gpsprof does not require root privileges, but it will run fine as root.
OPTIONS
The -f, --formatter option sets the plot type. Currently the following
plot types are defined:
space
Generate a scatterplot of fixes and plot probable error circles. This
data is only meaningful if the GPS is held stationary while gpsprof
is running. Various statistics about the fixes are listed at the
bottom. This is the default plot type.
polar
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.
polarunused
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.
polarused
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.
time
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.
instrumented
Plot instrumented profile. Plots various components of the total
latency between the GPS's fix time 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.
uninstrumented
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.
-?, -h, --help
Print a usage message and exit.
-d FILE, --dumpfile FILE
Dump the plot data, without attached gnuplot(1) code, to a specified
file for post-analysis.
-d LVL, --debug LVL
Sets debug level.
-l FILE, --logfile FILE
Dump the raw JSON reports collected from the device to the specified
FILE.
-n SEC, --wait SEC
Sets the number of seconds to sample. The default is 100. Most GPS
are configured to emit one fix per second, so 100 samples would then
span 100 seconds.
-r, --redo
Replot from a JSON logfile (such as -l, logfile produces) on standard
input. Both -n, --wait and -l, --logfile options are ignored when
this one is selected.
-S STR, --subtitle STR
Sets a text string to be included in the plot as a subtitle. This
will be below the title.
-t STR, --title STR
Sets a text string to be the plot title. This will replace the
default title.
-T TERM, --terminal TERM
Specify the terminal type setting in the gnuplot(1) code. Typical
usage is "-T png", or "-T pngcairo" telling gnuplot(1) to write a PNG
file. The default terminal is "x11".
Different installations of gnuplot(1) 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. The same terminal type may work very differently
on different distributions.
To see which terminal types your copy of gnuplot(1) supports:
gnuplot -e "set terminal"
ARGUMENTS
By default, clients collect data from the local gpsd daemon running on
localhost, using the default GPSD port 2947. The optional argument to any
client may override this behavior: [server[:port[:device]]]
For further explanation, and examples, see the ARGUMENTS section in the
gps(1) man page
SIGNALS
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.
EXAMPLES
To display the graph, use gnuplot(1) . Thus, for example, to display the
default spatial scatter plot on your x11 display, do this:
gpsprof | gnuplot -persist
To generate an image file:
gpsprof -T png | gnuplot > image.png
To generate a polar plot, and save the GPS data for further plots:
gpsprof -f polar -T jpeg -l polar.json | gnuplot > polar.png
Then to make the matching polarused and polarunused plots and pngs from
the just saved the GPS data:
gpsprof -f polarused -T jpeg -r < polar.json > polarused.plot
gnuplot < polarused.plot > polarused.png
gpsprof -f polarunused -T jpeg -r < polar.json > polarunused.plot
gnuplot < polarunused.plot > polarunused.png
You can split the pieces up, so you do not need to run the entire chain
at once. To allow tweaking settings without recollecting all the data.
Like this:
gpspipe -w -x 3600 ::/dev/ttyS0 > MY.raw
gpsdecode < MY.raw > MY.json
gpsprof -r -T pngcairo -t "MY Title" < MY.json > MY.plt
gnuplot MY.plt > MY.png
display MY.png
The gpspipe saves one hour of raw data from the local gpsd device
/dev/ttyS0 into MY.raw. It will take one hour to complete.
The gpsdecode converts the raw data in MY.raw into a gpsd JSON file
called MY.json.
The gpsprof reads MY.json and creates a gnuplot program in MY.plt.
The gnuplot executes the program in MY.plt and creates the image file
MY.png.
The display program paints MY.png on your desktop.
RETURN VALUES
0
on success.
1
on failure
SEE ALSO
gpsd(8), display(1), gnuplot(1), gpsctl(1), gps(1), libgps(3),
gpsprof(1), gpsfake(1).
RESOURCES
Project web site: <https://gpsd.io/>
COPYING
This file is Copyright 2013 by the GPSD project
SPDX-License-Identifier: BSD-2-clause
AUTHOR
Eric S. Raymond
GPSD, Version 3.24 2022-04-27 gpsprof(1)
mgpsd 3.24 - Generated Sat Dec 31 16:13:01 CST 2022