Documentation
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Overview ¶
Package rtcm decodes the RTCM 3.x differential-GNSS message framing — the protocol a GNSS base station broadcasts (over radio, NTRIP or a serial link) to feed real-time corrections to rovers. It is the third protocol in the GNSS triad alongside internal/nmea (gps_nmea_decode, the text output) and internal/ubx (ubx_decode, the u-blox binary input): a u-blox / Septentrio / Trimble receiver in a base/rover RTK setup emits RTCM3.
The GNSS-integrity angle: injecting forged RTCM corrections (a false 1005 reference-station position, or fabricated observables) is a known way to pull an RTK rover off its true fix. Decoding an RTCM stream lets an analyst see the reference-station id, the broadcast base-station ECEF position, and which message types / constellations a stream carries — surfacing an anomalous or spoofed correction source.
Wrap-vs-native judgement ¶
Native. The RTCM3 transport frame is a fixed, fully-public wire format (a 0xD3 preamble, 6 reserved bits, a 10-bit payload length, the payload, and a 24-bit CRC-24Q parity) defined in the RTCM 10403.x standard; the CRC-24Q polynomial (0x1864CFB) is the same Qualcomm CRC used across GNSS. Frame parsing + a bit reader + a CRC loop is a few hundred lines, so a runtime dependency would not be justified. stdlib only, no new go.mod dep.
What this package covers ¶
- RTCM3 transport framing: the 0xD3 preamble, 10-bit length, and the CRC-24Q (poly 0x1864CFB) over the whole frame, validated. A stream of back-to-back frames decodes to a list; leading non-preamble bytes are skipped so a mid-stream capture still parses. A frame whose CRC fails is surfaced with checksum_ok=false rather than dropped.
- Message-type identification (DF002, the first 12 payload bits) with a name for the common types: the 1001-1004 / 1009-1012 legacy RTK observables, 1005/1006 station ARP, 1007/1008/1033 antenna & receiver descriptors, 1019/1020/ 1042-1046 ephemerides, the 107x-112x MSM (multiple-signal message) families per constellation, and 1230 GLONASS code- phase biases. The reference-station id (DF003) is surfaced for the message types that carry it at bits 12-23.
- 1005 / 1006 Stationary RTK Reference Station ARP — the base-station antenna reference point as ECEF X / Y / Z (in metres, from the 38-bit 0.0001 m fields), the GPS / GLONASS / Galileo service indicators, and (1006 only) the antenna height. This is the message a spoofed-correction attack would tamper with, so it is bodied out.
What this package does NOT cover (deliberately out of scope) ¶
- The observable / ephemeris / MSM message bodies — these carry per-satellite pseudorange / carrier-phase / orbit data whose decode is large and constellation-specific; the frame is CRC-validated and the type + station id surfaced, with the payload left as raw hex rather than guessed. The station-ARP messages (1005/1006) are the ones bodied out because they carry the base position an integrity check cares about.
- RTCM 2.x (the older word-based framing) — a different, legacy protocol.
- NTRIP transport (the HTTP-like caster protocol that carries RTCM over the internet) — separate layer.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Message ¶
type Message struct {
MessageType int `json:"message_type"`
TypeName string `json:"type_name"`
Length int `json:"payload_length"`
ChecksumOK bool `json:"checksum_ok"`
ReferenceStationID *int `json:"reference_station_id,omitempty"`
StationARP *StationARP `json:"station_arp,omitempty"`
PayloadHex string `json:"payload_hex,omitempty"`
Notes []string `json:"notes,omitempty"`
}
Message is one decoded RTCM3 frame.
type StationARP ¶
type StationARP struct {
ECEFXm float64 `json:"ecef_x_m"`
ECEFYm float64 `json:"ecef_y_m"`
ECEFZm float64 `json:"ecef_z_m"`
GPSSupported bool `json:"gps_supported"`
GLONASSSupport bool `json:"glonass_supported"`
GalileoSupport bool `json:"galileo_supported"`
AntennaHeightM *float64 `json:"antenna_height_m,omitempty"`
}
StationARP is the decoded 1005 / 1006 Stationary RTK Reference Station Antenna Reference Point.
Source Files