269 lines
5 KiB
Text
269 lines
5 KiB
Text
.TH GPSFS 8
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.SH NAME
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gpsfs, gpsevermore \- GPS time and position service
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.SH SYNOPSIS
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.B aux/gpsfs
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[
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.B -d
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.I device
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]
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[
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.B -b
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.I baud
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]
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[
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.B -s
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.I srvname
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]
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[
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.B -m
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.I mntpt
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]
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.PP
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.B aux/gpsevermore
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[
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.B -d
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.I device
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]
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[
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.B -b
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.I baud
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]
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[
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.B -n
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.I baud
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]
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[
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.B -l
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.I location
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]
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.SH DESCRIPTION
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.B Aux/gpsfs
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reads an NMEA-compatible serial GPS (Global Positioning System)
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device and provides time and position
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through a file system, by default mounted on
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.B /mnt
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and implementing
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.BR /mnt/gps .
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.PP
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It implements four files in the
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.B gps
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directory:
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.BR position ,
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.BR time ,
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.BR satellites ,
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and
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.BR raw .
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.PP
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The read-only
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.B position
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file contains one line of information in 9 tab-separated fields:
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.TF "\fImagnetic deviation
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.PD
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.TP
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.I "fix quality
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0 means position data invalid, 1 means a 2D position is available, 2 means a 3D position is available.
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The value is 8, 9, or 10, respectively, when the fix data comes from a file rather than an actual GPS.
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.TP
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.I "zulu time
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universal coordinated time encoded as hhmmss followed by the character 'Z'.
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.TP
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.I "system time
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time and date converted to the format of
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.IR time (2).
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.TP
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.I longitude
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in degrees, east of Greenwich is positive, west negative.
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.TP
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.I latitude
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in degrees, positive is north, negative south of the equator.
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.TP
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.I altitude
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above sea level, in meters.
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.TP
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.I course
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degrees, clockwise from true north.
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.TP
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.I "ground speed
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in km/h
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.TP
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.I "magnetic deviation
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(not provided by all GPSs), in degrees, positive is westerly, negative easterly.
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.PP
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The read-only
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.B time
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file contains one line of information in 4 tab-separated fields:
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.TF "\fIsystem time
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.PD
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.TP
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.I "gps time
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in
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.IR time (2)
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format.
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.TP
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.I "gps time
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in
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.I nsec
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(see
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.IR time (2))
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format (ms accuracy).
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.TP
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.I "system time
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in
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.I nsec
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format. This is the system time at the time of the
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.I "gps time
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sample. The difference between this and the previous field is used in clock
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synchronization. See
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.IR timesync (8).
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.TP
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.I validity
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the character
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.B A
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meaning sample valid and usable for clock synchronization. The other values are
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not usable for clock sync:
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.B B
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means valid sample from file playback,
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.B V
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means invalid sample, and
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.B W
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means invalid playback sample.
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.PP
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The read-only
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.B satellites
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file contains information about the current satellite constellation. It consists
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of one line of general information, followed by zero or more lines, one for each satellite in use.
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The first line contains two fields:
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.TF "\fIsatellites in view
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.PD
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.TP
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.I "fix quality
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same as in the
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.B position
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file.
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.TP
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.I "satellites in view
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number of satellites above the horizon
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.PP
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Subsequent lines have four fields:
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.TF "\fIelevation
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.PD
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.TP
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.I prn
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satellite ID
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.TP
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.I elevation
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above the horizon, degrees.
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.TP
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.I azimuth
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direction, degrees from true north
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.TP
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.I snr
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Signal to noise ratio, 0 - 99 dB
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.PP
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The contents of these files are refreshed once per second when reading from an actual GPS,
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and once per 100 ms (giving a speed up of a factor 10) when playing back from file.
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.PP
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The read-only
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.B raw
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file can be read to obtain a copy of the raw NMEA GPS output.
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.I Gpsfs
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keeps an internal buffer of 8KB, so the reader must keep up with the output
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(typically 500 or so bytes per second).
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.PP
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The
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.B \-d
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flag establishes the device the GPS samples are read from. If the device file is not
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a serial interface,
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.I gpsfs
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assumes playback from file and modifies quality parameters as such.
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.PP
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The
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.B \-b
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flag specifies the baud rate of the serial line. The standard baud rate for NMEA
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GPS is 4800 baud, but many device allow changing to higher speeds.
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.PP
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The
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.B \-s
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flag specifies the name under which the
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.I gpsfs
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service is posted in
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.BR /srv .
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.PP
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The
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.B \-m
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flag specifies a mount other than
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.BR /mnt .
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.SS Evermore
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.B Aux/gpsevermore
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is used to configure GPSs using an Evermore chipset.
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.PP
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The
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.B \-d
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flag specifies the serial device to the GPS.
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.PP
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The
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.B \-b
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flag specifies the baud rate of the serial line. The standard baud rate for NMEA
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GPS is 4800 baud, but many device allow changing to higher speeds.
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.PP
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The
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.B \-n
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flag specifies the speed to set the GPS to. When the command finishes, the
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GPS should be read (and configured) at the new speed.
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.PP
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The
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.B \-l
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flag is sued to specify the location to initialize the GPS to. The format is
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.B dd:mm:ssX
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or
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.B dd:mm.mmmX
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or
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.BR dd.dddX ,
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where
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.B dd
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stands for degrees (one or more digits),
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.B mm
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for minutes and
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.B ss
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for seconds of arc.
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.B X
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is one of
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.BR W ,
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.BR E ,
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.B N
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or
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.BR S .
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Longitudes come with
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.B W
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or
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.BR E ,
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latitudes with
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.B N
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or
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.BR S .
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The
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.B \-l
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flag is followed by two such fields, one for longitude, one for latitude. They may be
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given in a single argument (separated by white space), or in two arguments, in either order.
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Initialization time is taken from
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.IR time (2).
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.SH "SEE ALSO
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.IR timesync (8),
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.IR time (2)
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.SH FILES
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.TF /mnt/gps/satellites
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.TP
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.B /mnt/gps/position
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position, time, speed and heading
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.TP
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.B /mnt/gps/satellites
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satellites in view
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.TP
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.B /mnt/gps/time
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GPS time (millisecond accuracy)
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.TP
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.B /dev/eia0
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default GPS device
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.SH SOURCE
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.B /sys/src/cmd/aux/gps
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