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TraceNav VRTK converts state-space inputs into real-time observation corrections for every active region. Instead of relaying a single physical base station, TraceNav synthesizes a virtual base centered on each rover using precise global models. Once a rover delivers its first valid GGA, TraceRouter promotes the session from TraceAssist Ephemeris to VRTK mode and begins streaming the generated OSR data.

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TraceNav VRTK – Synthetic OSR Generation Overview

TraceVRTK operates as an SSR-to-OSR engine. By fusing orbit, clock, bias, ionospheric, and tropospheric models with the rover’s live position, it synthesizes a virtual reference station in software and outputs standard RTCM observation frames.

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Synthetic OSR generation

TraceNav ingests State-Space Representation (SSR) feeds—orbital clocks, biases, and atmospheric models—and transforms them into Observation-Space Representation (OSR) corrections tailored to each rover.
  • SSR inputs:
    • Orbit, clock, code bias, and phase bias messages (OCB) from commercial SSR providers
    • Global ionospheric grids
    • Real-time tropospheric delay models
  • Rover context: The NMEA GGA supplied by the rover gives TraceRouter an approximate position, velocity, and height to anchor the synthetic base.
  • Output: RTCM MSM4 (and supporting) frames that mimic a local reference station colocated with the rover.
Because VRTK builds virtual bases on demand, rovers experience uniform performance across the coverage area without needing to home onto a specific physical station.

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Processing pipeline

  1. Receive SSR packets – orbit, clock, bias, ionosphere, and troposphere data arrive continuously for all enabled constellations.
  2. Resolve satellite state – TraceNav evaluates the satellite positions and corrections at the current epoch for the rover’s reported location.
  3. Generate virtual observations – SSR parameters are converted into OSR pseudorange, carrier-phase, and Doppler adjustments per satellite.
  4. Assemble RTCM frames – Corrections are packaged into MSM4 observation messages (1074, 1084, 1094, 1124, etc.) plus supporting station metadata (1005/1006, 1033, 1230).
  5. Serve over NTRIP 1.0 – The synthetic stream is forwarded through TraceRouter, so rovers consume it exactly like any other correction feed.

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Session lifecycle

1

Session created

Client authenticates with TraceRouter over NTRIP. A session ID and default region are assigned instantly.
2

Ephemeris warmup

While no GGA is received, TraceAssist Ephemeris repeats satellite orbital parameters every 5 seconds to prime the receiver.
3

First GGA received

TraceRouter evaluates the reported position, selects the nearest virtual reference service (VRS) cell, and switches the mountpoint.
4

VRTK streaming

The rover receives synthetic RTCM MSM4 corrections (1 Hz by default) covering all enabled constellations plus the supporting station messages.
5

Continuous optimization

As the rover moves, GGA updates keep the session attached to the optimal base or VRS region. Loss of GGA can trigger automatic fallbacks (configurable).
Send NMEA GGA at a 1–5 second interval. This helps TraceRouter maintain low baseline distances and anticipate region handoffs while staying within bandwidth constraints.

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RTCM message set

Msg TypeConstellationDescriptionCadence
1005 / 1006AllReference station ARP coordinates (with optional height)1 per minute
1033AllAntenna descriptor, firmware ID, serial1 per hour
1074GPSMSM4 observations (code, phase, Doppler, C/N₀)1 Hz
1084GLONASSMSM4 observations1 Hz
1094GalileoMSM4 observations1 Hz
1124BeiDouMSM4 observations1 Hz
1230GLONASSCode-phase bias for inter-frequency calibration30 s
Optional message types (MSM5/MSM7, SBAS, QZSS) are available on request for compatible receivers.

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Stream anatomy

<timestamp_ms> <msg_type> <station_id> <length_bytes> <hex_payload>
1760641557250 1074 10 197 d300bf43…c31
1760641557250 1084 10  86 d3005043…906
1760641557250 1094 10 234 d300e444…76
1760641557250 1124 10 167 d300a146…26
Use this structure when debugging logs from TraceRouter or your rover. Payloads are standard RTCM binary frames.

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Integration checklist

  • Client: Any NTRIP 1.0-compatible rover, SDK, or custom socket client.
  • Transport: Persistent TCP connection to ntrip.tracenav.net:2101.
  • Mountpoint: Always connect to /tracenav; TraceRouter handles regional routing after authentication and GGA handoff.
  • Upstream GGA: Recommended 1–2 second interval for high-dynamic assets, 5 seconds for survey rovers.
  • Reconnect logic: Implement exponential backoff on disconnects; TraceRouter preserves session metadata for 60 seconds.

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Monitoring & analytics

  • TraceNav dashboard → Device → Live Sessions: verifies VRTK mode, mountpoint, and base station.
  • Message counters: confirm MSM4 messages per second per constellation.
  • Correction age: should stay < 5 seconds with healthy connectivity.
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