'\" t
.\"     Title: gpsdecode
.\"    Author: [see the "AUTHOR" section]
.\" Generator: DocBook XSL Stylesheets vsnapshot <http://docbook.sf.net/>
.\"      Date: 6 December 2020
.\"    Manual: GPSD Documentation
.\"    Source: The GPSD Project
.\"  Language: English
.\"
.TH "GPSDECODE" "1" "6 December 2020" "The GPSD Project" "GPSD Documentation"
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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 [\-?] [\-\-ais] [\-\-decode] [\-\-debug\ \fILVL\fR] [\-\-encode] [\-\-help] [\-\-json] [\-\-minlength] [\-\-nmea] [\-\-split24] [\-\-types\ \fItypelist\fR] [\-\-unscaled] [\-\-verbose] [\-\-version] [\-c] [\-d] [\-D\ \fILVL\fR] [\-e] [\-h] [\-j] [\-m] [\-n] [\-s] [\-t\ \fItypelist\fR] [\-u] [\-v] [\-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
\fB\-?\fR, \fB\-h\fR, \fB\-\-help\fR
.RS 4
Output a usage mssage, then exit\&.
.RE
.PP
\fB\-c\fR, \fB\-\-json\fR
.RS 4
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 (\fB\-u\fR
is forced)\&. Strings are unpacked from six\-bit to full ASCII
.RE
.PP
\fB\-d\fR, \fB\-\-decode\fR
.RS 4
Decode packets presented on standard input to standard output\&. This is the default behavior\&.
.RE
.PP
\fB\-D LVL\fR, \fB\-\-debug LVL\fR
.RS 4
Set the debug verbosity level to LVL\&. It is mainly of interest to for troubleshooting\&.
.RE
.PP
\fB\-e\fR, \fB\-\-encode\fR
.RS 4
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\&.
.RE
.PP
\fB\-j\fR, \fB\-\-json\fR
.RS 4
Sets the output dump format to JSON (the default behavior)\&.
.RE
.PP
\fB\-m\fR, \fB\-\-minlength\fR
.RS 4
Dump minimum lengths for each packet type in the input (ignoring comment packets)\&. This is probably of interest only to GSD developers\&.
.RE
.PP
\fB\-n\fR, \fB\-\-nmea\fR
.RS 4
Dump the generated pseudo\-NME0183\&.
.RE
.PP
\fB\-s\fR, \fB\-\-split24\fR
.RS 4
Report AIS Type 24 sentence halves separately rather than attempting to aggregate them\&.
.RE
.PP
\fB\-t TYPES\fR, \fB\-\-types TYPES\fR
.RS 4
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\&.
.RE
.PP
\fB\-u\fR, \fB\-\-unsscaled\fR
.RS 4
Suppress scaling of AIS data to float quantities and text expansion of numeric codes\&. A dump with this option is lossless\&.
.RE
.PP
\fB\-v\fR, \fB\-\-verbose\fR
.RS 4
Dump textual packets to output as they are received on input, immediately preceding corresponding output\&.
.RE
.PP
\fB\-V\fR, \fB\-\-version\fR
.RS 4
Print version number, then exit\&.
.RE
.SH "AIS DSV FORMAT"
.PP
With the
\fB\-c, \-\-ais\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),
\fBlibgpsmm\fR(3),
\fBgpsprof\fR(1),
\fBgpsfake\fR(1),
.SH "AUTHOR"
.PP
Eric S\&. Raymond
<esr@thyrsus\&.com>\&.