RTCM 3 frame structure
A frame starts with 0xD3, includes a payload length, then message type and fields, and ends with CRC24Q. The CRC allows corrupted frames to be rejected.
TCP is a byte stream. One read can contain a partial frame or several frames. A parser retains incomplete bytes, searches for the preamble, validates length, waits for completion, and verifies the CRC.
Distribution does not require full decoding. The caster forwards valid byte buffers while a parallel parser extracts selected monitoring information.
Reference and equipment messages
1005 and 1006 carry signed ECEF station coordinates; 1006 adds antenna height. Strict payload-length checks prevent out-of-range bit reads on partial data.
1007 and 1008 describe the antenna, and 1033 can add receiver information. Availability depends on base configuration.
These fields support monitoring but do not replace a verified station log. Generic or empty descriptors only show what the receiver transmitted.
MSM and GNSS constellations
Multiple Signal Messages represent satellite and signal observations with a common structure. Separate message families serve GPS, GLONASS, Galileo, BeiDou, QZSS, and SBAS.
MSM4, MSM5, MSM6, and MSM7 provide different detail and bandwidth. Choice depends on rover compatibility and measured service benefit.
Sourcetable declarations should match the actual stream. Monitoring can confirm expected message families over time.
NTRIP transport and integrity
NTRIP begins with text headers and then carries raw RTCM. The exact header/body boundary matters. Appending line breaks or decoding the stream as UTF-8 corrupts frames.
Byte-array networking produces the same payload on Windows and Debian. Suspected encoding failures are commonly framing, buffering, response, or remote-disconnection issues.
Source age and byte counters are simple operational measures. Precise latency analysis may require GNSS message timestamps and synchronized system time.
RTCM FAQ
Are RTCM and RINEX equivalent?
No. RTCM is optimized for real-time delivery, while RINEX is a file exchange format for post-processing and archiving.
Why is RTCM unreadable in a terminal?
RTCM is binary. Rendering it as text produces arbitrary characters. Use a decoder or hexadecimal view.
Does message 1006 contain latitude directly?
No. It carries ECEF X, Y, and Z plus antenna height. Software converts the ECEF coordinates to geodetic latitude, longitude, and ellipsoidal height.