rtcmdecode - decode RTCM104 streams into a readable format

This tool is a decoder for RTCM-104, an obscure and complicated serial protocol used for broadcasting pseudorange corrections from differential-GPS reference stations. RTCM-104 is expected on standard input; an equivalent, 100%-information-preserving text format is written to standard output.

You can use this tool with nc(1) to examine RTCM feeds from DGPSIP servers.

The decoder dump format is described in rtcm(5); these lines go to standard output. As well as data the decoder also prints decoder status messages to standard error, as necessary.

The -d option tells the program to decode RTCM-104 presented on standard input to a text dump in the format of rtcm-104(5) on standard output. This is the default behavior.

The -e option option tells the program to encode a text dump in the format of rtcm-104(5) to standard output.

The -v option sets a verbosity level. It is mainly of interest to developers.

The applicable standard is RTCM Recommended Standards for Differential NAVSTAR GPS Service RTCM Paper 194-93/SC 104-STD.

Ordering instructions are accessible from the website of the Radio Technical Commission for Maritime Services: http://www.rtcm.org/ under "Publications".

RTCM-104 represents floating-point quantities as an integer multiple of a fixed scale factor. Editing an RTCM-104 dump can produce numbers that are not an integer multiple of the scale factor for their field. If you do this, the value actually packed into binary RTCM-104 will be rounded down to the nearest scale unit, and dumping will show slightly different numbers than those you entered.

The decoder logic is sufficiently convoluted to confuse some compiler optimizers, notably in GCC 3.x at -O2, into generating bad code.

gpsd(8), xgps(1), libgps(3), libgpsd(3), gpsprof(1), gpsfake(1), rtcm-104(5).

Eric S. Raymond <esr@thyrsus.com>. This is a somewhat hacked version of an RTCM decoder originally written by Wolfgang Rupprecht. There is a project page for gpsd here: http://gpsd.berlios.de/.