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 [OPTIONS] [server[:port[:device]]]
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11       gpsprof -h
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13       gpsprof -V
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DESCRIPTION

16       gpsprof performs accuracy, latency, skyview, and time drift profiling
17       on a GPS. It emits to standard output a GNUPLOT program that draws one
18       of several illustrative graphs. It can also be told to emit the raw
19       profile data.
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21       Information from the default spatial plot it provides can be useful for
22       characterizing position accuracy of a GPS.
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24       gpsprof uses instrumentation built into gpsd. It can read data from a
25       local or remote running gpsd. Or it can read data from a saved logfile.
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27       gpsprof is designed to be lightweight and use minimal host resources.
28       No graphics subsystem needs to be installed on the host running
29       gpsprof. Simply copy the resultant plot file to another host to be
30       rendered with gnuplot(1).
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32       gpsprof does not require root privileges, but it will run fine as root.
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OPTIONS

35       The -f, --formatter option sets the plot type. Currently the following
36       plot types are defined:
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38       space
39           Generate a scatterplot of fixes and plot probable error circles.
40           This data is only meaningful if the GPS is held stationary while
41           gpsprof is running. Various statistics about the fixes are listed
42           at the bottom. This is the default plot type.
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44       polar
45           Generate a heat map of reported satellite Signal to Noise Ratio
46           (SNR) using polar coordinates. A colored dot is plotted for each
47           satellite seen by the GPS. The color of dot corresponds to the SNR
48           of the satellite. The dots are plotted by azimuth and elevation.
49           North, azimuth 0 degrees, is at the top of the plot. Directly
50           overhead, elevation of 90 degrees, is plotted at the center. Useful
51           for analyzing the quality of the skyview as seen by the GPS.
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53       polarunused
54           Similar to the polar plot, but only unused satellites are plotted.
55           Useful for seeing which parts of the antenna skyview are
56           obstructed, degraded, below the GPS elevation mask, or otherwise
57           rejected.
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59       polarused
60           Similar to the polar plot, but only satellites used to compute
61           fixes are plotted. Useful for seeing which parts of the antenna
62           skyview are being used in fixes.
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64       time
65           Plot delta of system clock (NTP corrected time) against GPS time as
66           reported in PPS messages. The X axis is sample time in seconds from
67           the start of the plot. The Y axis is the system clock delta from
68           GPS time.
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70       instrumented
71           Plot instrumented profile. Plots various components of the total
72           latency between the GPS’s fix time and when the client receives the
73           fix.
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75       For purposes of the description, below, start-of-reporting-cycle (SORC)
76       is when a device’s reporting cycle begins. This time is detected by
77       watching to see when data availability follows a long enough amount of
78       quiet time that we can be sure we’ve seen the gap at the end of the
79       sensor’s previous report-transmission cycle. Detecting this gap
80       requires a device running at 9600bps or faster.
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82       Similarly, EORC is end-of-reporting-cycle; when the daemon has seen the
83       last sentence it needs in the reporting cycle and ready to ship a fix
84       to the client.
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86       The components of the instrumented plot are as follows:
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88       Fix latency
89           Delta between GPS time and SORC.
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91       RS232 time
92           RS232 transmission time for data shipped during the cycle (computed
93           from character volume and baud rate).
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95       Analysis time
96           EORC, minus SORC, minus RS232 time. The amount of real time the
97           daemon spent on computation rather than I/O.
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99       Reception time
100           Shipping time from the daemon to when it was received by gpsprof.
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102       Because of RS232 buffering effects, the profiler sometimes generates
103       reports of ridiculously high latencies right at the beginning of a
104       session. The -m option lets you set a latency threshold, in multiples
105       of the cycle time, above which reports are discarded.
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107       uninstrumented
108           Plot total latency without instrumentation. Useful mainly as a
109           check that the instrumentation is not producing significant
110           distortion. The X axis is sample time in seconds from the start of
111           the plot. The Y axis is latency in seconds. It only plots times for
112           reports that contain fixes; staircase-like artifacts in the plot
113           are created when elapsed time from reports without fixes is lumped
114           in.
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116       -?, -h, --help
117           Print a usage message and exit.
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119       -d FILE, --dumpfile FILE
120           Dump the plot data, without attached gnuplot(1) code, to a
121           specified file for post-analysis.
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123       -d LVL, --debug LVL
124           Sets debug level.
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126       -l FILE, --logfile FILE
127           Dump the raw JSON reports collected from the device to the
128           specified FILE.
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130       -n SEC, --wait SEC
131           Sets the number of seconds to sample. The default is 100. Most GPS
132           are configured to emit one fix per second, so 100 samples would
133           then span 100 seconds.
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135       -r, --redo
136           Replot from a JSON logfile (such as -l, logfile produces) on
137           standard input. Both -n, --wait and -l, --logfile options are
138           ignored when this one is selected.
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140       -S STR, --subtitle STR
141           Sets a text string to be included in the plot as a subtitle. This
142           will be below the title.
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144       -t STR, --title STR
145           Sets a text string to be the plot title. This will replace the
146           default title.
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148       -T TERM, --terminal TERM
149           Specify the terminal type setting in the gnuplot(1) code. Typical
150           usage is "-T png", or "-T pngcairo" telling gnuplot(1) to write a
151           PNG file. The default terminal is "x11".
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153           Different installations of gnuplot(1) will support different
154           terminal types. Different terminal types may work better for you
155           than other ones. "-T png" will generate PNG images. Use "-T jpeg"
156           to generate JPEG images. "-T pngcairo" often works best, but is not
157           supported by some distributions. The same terminal type may work
158           very differently on different distributions.
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160           To see which terminal types your copy of gnuplot(1) supports:
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162           gnuplot -e "set terminal"
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ARGUMENTS

165       By default, clients collect data from the local gpsd daemon running on
166       localhost, using the default GPSD port 2947. The optional argument to
167       any client may override this behavior: [server[:port[:device]]]
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169       For further explanation, and examples, see the ARGUMENTS section in the
170       gps(1) man page
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SIGNALS

173       Sending SIGUSR1 to a running instance causes it to write a completion
174       message to standard error and resume processing. The first number in
175       the startup message is the process ID to signal.
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EXAMPLES

178       To display the graph, use gnuplot(1) . Thus, for example, to display
179       the default spatial scatter plot on your x11 display, do this:
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181           gpsprof | gnuplot -persist
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183       To generate an image file:
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185           gpsprof -T png | gnuplot > image.png
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187       To generate a polar plot, and save the GPS data for further plots:
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189           gpsprof -f polar -T jpeg -l polar.json | gnuplot > polar.png
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191       Then to make the matching polarused and polarunused plots and pngs from
192       the just saved the GPS data:
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194           gpsprof -f polarused -T jpeg -r < polar.json > polarused.plot
195           gnuplot < polarused.plot > polarused.png
196           gpsprof -f polarunused -T jpeg -r < polar.json > polarunused.plot
197           gnuplot < polarunused.plot  > polarunused.png
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199       You can split the pieces up, so you do not need to run the entire chain
200       at once. To allow tweaking settings without recollecting all the data.
201       Like this:
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203           gpspipe -w -x 3600 ::/dev/ttyS0 > MY.raw
204           gpsdecode  < MY.raw > MY.json
205           gpsprof -r -T pngcairo -t "MY Title" < MY.json > MY.plt
206           gnuplot MY.plt > MY.png
207           display MY.png
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209       The gpspipe saves one hour of raw data from the local gpsd device
210       /dev/ttyS0 into MY.raw. It will take one hour to complete.
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212       The gpsdecode converts the raw data in MY.raw into a gpsd JSON file
213       called MY.json.
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215       The gpsprof reads MY.json and creates a gnuplot program in MY.plt.
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217       The gnuplot executes the program in MY.plt and creates the image file
218       MY.png.
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220       The display program paints MY.png on your desktop.
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RETURN VALUES

223       0
224           on success.
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226       1
227           on failure
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SEE ALSO

230       gpsd(8), display(1), gnuplot(1), gpsctl(1), gps(1), libgps(3),
231       libgpsmm(3), gpsprof(1), gpsfake(1).
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RESOURCES

234       Project web site: https://gpsd.io/
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COPYING

237       This file is Copyright 2013 by the GPSD project
238       SPDX-License-Identifier: BSD-2-clause
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AUTHOR

241       Eric S. Raymond
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245GPSD, Version 3.24                2022-04-27                        GPSPROF(1)
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