RTCM3 Messages
The LC29H(DA) accepts RTCM3.x correction messages as input for RTK rover operation. The LC29H(BS) outputs RTCM3.x messages for base station use. RTCM messages are binary-framed (not NMEA) and share the same UART port.
RTCM3 Binary Framing
Section titled “RTCM3 Binary Framing”RTCM3 messages use a binary frame format distinct from NMEA text sentences:
D3 [length_hi] [length_lo] [message_data...] [CRC24Q_hi] [CRC24Q_mid] [CRC24Q_lo]| Field | Bytes | Description |
|---|---|---|
| Preamble | 1 | 0xD3 — identifies the start of an RTCM3 frame |
| Reserved | 6 bits | Reserved, set to 0 |
| Length | 10 bits | Message data length (0–1023 bytes) |
| Message Data | variable | RTCM3 message content |
| CRC | 3 | CRC-24Q integrity check |
Reference Station Messages
Section titled “Reference Station Messages”| Message | Type | Description |
|---|---|---|
| 1005 | Stationary ARP | Reference station antenna reference point (ECEF X/Y/Z) |
Message 1005 provides the base station’s known position in Earth-Centered Earth-Fixed coordinates. This is the foundation for all differential corrections — the rover uses this position to compute its own baseline vector.
Satellite Ephemeris Messages
Section titled “Satellite Ephemeris Messages”| Message | Constellation | Description |
|---|---|---|
| 1019 | GPS | GPS satellite ephemeris parameters |
| 1020 | GLONASS | GLONASS satellite ephemeris parameters |
| 1042 | BeiDou | BDS satellite ephemeris parameters |
| 1044 | QZSS | QZSS satellite ephemeris parameters |
| 1046 | Galileo | Galileo I/NAV satellite ephemeris parameters |
MSM4 — Compact Observables
Section titled “MSM4 — Compact Observables”MSM4 messages include pseudorange and carrier-phase observables. Suitable for most RTK applications with moderate bandwidth.
| Message | Constellation |
|---|---|
| 1074 | GPS MSM4 |
| 1084 | GLONASS MSM4 |
| 1094 | Galileo MSM4 |
| 1114 | QZSS MSM4 |
| 1124 | BeiDou MSM4 |
MSM7 — Full Observables
Section titled “MSM7 — Full Observables”MSM7 messages include all observable types at full resolution (code + carrier phase + Doppler + SNR). Higher bandwidth than MSM4 but provides additional signal quality information.
| Message | Constellation |
|---|---|
| 1077 | GPS MSM7 |
| 1087 | GLONASS MSM7 |
| 1097 | Galileo MSM7 |
| 1117 | QZSS MSM7 |
| 1127 | BeiDou MSM7 |
RTCM Output Mode Selection
Section titled “RTCM Output Mode Selection”Use PAIR432 to select MSM4 or MSM7 output on the BS variant:
| Mode | PAIR432 Value | Messages Output |
|---|---|---|
| Disabled | -1 | No RTCM output |
| MSM4 | 0 | 1005 + ephemeris + MSM4 (1074/1084/1094/1114/1124) |
| MSM7 | 1 | 1005 + ephemeris + MSM7 (1077/1087/1097/1117/1127) |
Antenna reference point (1005) and ephemeris messages are independently controlled via PAIR434 and PAIR436.
Common NTRIP Caster Messages
Section titled “Common NTRIP Caster Messages”When connecting to public NTRIP casters like rtk2go.com, the correction stream typically contains:
| Message | Description | Typical Rate |
|---|---|---|
| 1005 | Base station position (ECEF) | Every 10 seconds |
| 1074/1077 | GPS observations | Every 1 second |
| 1084/1087 | GLONASS observations | Every 1 second |
| 1094/1097 | Galileo observations | Every 1 second |
| 1124/1127 | BeiDou observations | Every 1 second |
| 1230 | GLONASS code-phase bias | Every 10 seconds |