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'\" t
.\" Title: gpsdecode
.\" Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\" Date: 13 Jul 2005
.\" Manual: GPSD Documentation
.\" Source: The GPSD Project
.\" Language: English
.\"
.TH "GPSDECODE" "1" "13 Jul 2005" "The GPSD Project" "GPSD Documentation"
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.\" * MAIN CONTENT STARTS HERE *
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.SH "NAME"
gpsdecode \- decode GPS, RTCM or AIS streams into a readable format
.SH "SYNOPSIS"
.HP \w'\fBgpsdecode\fR\ 'u
\fBgpsdecode\fR [\-c] [\-d] [\-e] [\-j] [\-s] [\-t\ \fItypelist\fR] [\-u] [\-v] [\-D\ \fIdebuglevel\fR] [\-V]
.SH "DESCRIPTION"
.PP
This tool is a batch\-mode decoder for NMEA and various binary packet formats associated with GPS, AIS, and differential\-correction services\&. It produces a JSON dump on standard output from binary on standard input\&. The JSON is the same format documented in
\fBgpsd\fR(8); this tool uses the same decoding logic as gpsd, but with a simpler interface intended for batch processing of data files\&.
.PP
All sensor\-input formats known to the GPSD project can be decoded by this tool\&. These include: NMEA, AIVDM (the NMEA\-derived sentence format used by AIS, the marine Automatic Identification System), RTCM2, and all supported GPS binary formats (notably including SiRF)\&. See
\fBgpsd\fR(8)
for applicable standards and known limitations of the decoding logic\&.
.PP
You can use this tool with
\fBnc\fR(1)
to examine AIS feeds from AIS pooling services, RTCM feeds from RTCM receivers or NTRIP broadcasters\&.
.SH "OPTIONS"
.PP
The
\fB\-d\fR
option tells the program to decode packets presented on standard input to standard output\&. This is the default behavior\&.
.PP
The
\fB\-j\fR
explicitly sets the output dump format to JSON (the default behavior)\&.
.PP
The
\fB\-e\fR
option option tells the program to encode JSON on standard input to JSON on standard output\&. This option is only useful for regression\-testing of the JSON dumping and parsing code\&.
.PP
The
\fB\-s\fR
option option tells the program to report AIS Type 24 sentence halves separately rather than attempting to aggregate them\&.
.PP
The
\fB\-t\fR
accepts a comma\-separated list of numeric types\&. Packets with a numeric AIS, RTCM2, or RTCM3 type are passed through and output only if they match a type in the list\&. Packets of other kinds (in particular GPS packets) are passed through unconditionally\&.
.PP
The
\fB\-u\fR
suppresses scaling of AIS data to float quantities and text expansion of numeric codes\&. A dump with this option is lossless\&.
.PP
The
\fB\-v\fR
enables dumping of textual packets to output as they are received on input, immediately preceding corresponding output\&.
.PP
The
\fB\-c\fR
sets the AIS dump format to separate fields with an ASCII pipe symbol\&. Fields are dumped in the order they occur in the AIS packet\&. Numerics are not scaled (\-u is forced)\&. Strings are unpacked from six\-bit to full ASCII
.PP
The
\fB\-V\fR
option directs the program to emit its version number, then exit\&.
.PP
The
\fB\-D\fR
option sets a debug verbosity level\&. It is mainly of interest to developers\&.
.SH "AIS DSV FORMAT"
.PP
With the
\fB\-c\fR
option, dump lines are values of AIS payload fields, pipe\-separated, in the order that they occur in the payload\&. Spans of fields expressing a date are emitted as an ISO8601 timestamp (look for colons and the trailing Z indicating Zulu/UTC time), and the 19\-bit group of TDMA status fields found at the end of message types 1\-4 are are dumped as a single unsigned integer (in hex preceded by "0x")\&. Unused regional\-authority fields are also dumped (in hex preceded by "0x")\&. Variable\-length binary fields are dumped as an integer bit length, followed by a colon, followed by a hex dump\&.
.SH "SEE ALSO"
.PP
\fBgpsd\fR(8),
\fBgpsctl\fR(1),
\fBgpsdctl\fR(8),
\fBgps\fR(1),
\fBlibgps\fR(3),
\fBlibgpsd\fR(3),
\fBgpsprof\fR(1),
\fBgpsfake\fR(1),
.SH "AUTHOR"
.PP
Eric S\&. Raymond
<esr@thyrsus\&.com>\&.
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