TECHNICAL GUIDE
Dead reckoning carries a navigation state through short GNSS gaps, but its error grows. Start with the sky condition, then choose between standard RTK, integrated RTK + DR, and tightly coupled GNSS/INS.
Measured across 58.8 km of highway, residential streets, urban canyon, and tunnel — with no wheel-speed input.
START WITH THE OPERATING CONDITION
Choose the condition that dominates the route. GNSS dead reckoning can preserve a continuous state through a short gap, but the right system depends on whether satellite observations are absent, degraded, or still trustworthy.
System fit
Integrated RTK + DR for a short, moving outage.
Why
The IMU keeps position, velocity, and attitude propagating while GNSS is unavailable. Error grows with distance until a trustworthy RTK Fixed observation returns.
Verify
Longest blackout distance · acceptable exit error · where RTK Fixed reliably returns
System fit
Improve antenna and RF first; consider tightly coupled GNSS/INS when measurements remain usable.
Why
An IMU added after a finished, multipath-biased GNSS position cannot recover a correct absolute solution or turn Float into Fixed.
Verify
Time spent in Float · multipath pattern · access to raw or quality-aware measurements
System fit
Validate standard RTK before adding a DR variant.
Why
If the receiver stays RTK Fixed, there is no continuity gap for dead reckoning to bridge. An IMU may still help with attitude or output rate.
Verify
Fixed availability · actual position error · whether attitude or a faster output is required
System fit
This is an output and attitude requirement, not an outage problem.
Why
IMU propagation fills the interval between GNSS updates and carries short-term angular motion, but it does not create drift-free absolute heading by itself.
Verify
GNSS solution rate · fused navigation output rate · required heading reference
KALMIX FIELD TEST
Three measured conditions lead to three different decisions: carry continuity through a complete blackout, do not expect an IMU to repair sustained Float, and do not add DR where RTK stays Fixed.
TUNNEL · COMPLETE BLACKOUT
2.447 km
Complete-blackout tunnel pass.
CEP50 1.9 m · R95 3.727 m
DR replaced a loss of continuity with a propagated navigation state; it did not preserve RTK accuracy.
For a downstream controller, a gradually growing error is usually easier to handle than a sudden loss or jump in position. The acceptance question is exit error and how soon trustworthy RTK Fixed returns—not the availability percentage.
GT-02 CONFIGURATION COMPARISON
WITH DR · DR COASTINGThe evaluated configurations maintained a continuous tunnel track.
WITHOUT DR · NO CONTINUOUS TRACKThe evaluated configurations returned only sparse tunnel points.
ACROSS THE COMPARED ROUTE · 100% vs 95.83–96.03% Valid-Epoch Completeness
OVERHEAD OBSTRUCTION · DEGRADED SKY
97.85% RTK Float across 9,981 epochs
7.481 km test stretch · CEP50 2.86 m · R95 7.42 m
The IMU did not turn Float into Fixed.
RESIDENTIAL · RTK CONTROL
100% RTK Fixed across all evaluated residential epochs
2.83 km residential comparison segment
No coasting was required in this segment.
THREE SYSTEM ROLES, NOT ONE IMU LADDER
GNSS/IMU sensor fusion covers systems built for different jobs. Fusion depth, aiding, motion constraints, and inertial class change together—not in a single ranked order.
| System role | How it fuses | Best fit | Boundary | Kalmix path |
|---|---|---|---|---|
| Integrated RTK + DR COMPLETE BLACKOUT | Industrial-grade 6-axis MEMS propagating a finished GNSS solution. | Short moving outages; higher-rate fused output | Cannot correct a multipath-biased finished GNSS position | SCOUT SERIES AVAILABLE NOW |
| Tightly Coupled GNSS/INS SUSTAINED DEGRADED SKY | Automotive-grade MEMS with raw-measurement GNSS/INS fusion. | Partial sky where some observations still carry information | Still needs usable satellite or external constraints | EXPLORER COMING SOON |
| FOG GNSS/INS Reference REFERENCE & EVALUATION | Fibre-optic GNSS/INS for reference trajectories and uncertainty evaluation. | Reference trajectories and system evaluation | Not a retail upgrade path for an integrated receiver | FORERUNNER COMING SOON |
If the sky stays healthy and RTK remains Fixed, standard RTK is the positioning baseline; add an IMU only when attitude or a higher-rate fused output is itself required.
USEFUL OUTPUTS, CLEAR INTEGRATION CONDITIONS
A fused state is only as usable as its measurements, mounting geometry, calibration, and motion assumptions.
Carries a continuous position and velocity state through a short outage; error grows until a trusted update returns.
Adds roll, pitch, and short-term yaw propagation; it does not create drift-free absolute heading.
Fills intervals between GNSS updates with a fused state; it does not increase the GNSS observation rate.
| Course over ground | Single-antenna direction of travel while moving; not the orientation of a stationary body. |
|---|---|
| Baseline heading | Dual-antenna orientation while GNSS is available; its meaning depends on antenna geometry and mounting. |
| IMU yaw propagation | Short-term change from gyro integration; it needs motion or an absolute reference to limit drift. |
The IMU carries the state. Trusted observations close the loop.
DECISION BOUNDARIES
START WITH GNSS STATE, NOT THE SCENE
This is often degraded GNSS, not a pure blackout. Improve antenna/RF first; use quality-aware logic or evaluate tightly coupled GNSS/INS when raw measurements remain usable.
A single antenna plus a six-axis IMU cannot supply drift-free stationary yaw. Use dual-antenna GNSS or another absolute heading reference.
Full-6DoF aircraft motion and changing device or body orientation invalidate ground-vehicle assumptions. Use platform-specific GNSS/INS or PDR carrying-mode logic.
Without an external constraint, inertial error continues accumulating. Consider vision, UWB, LiDAR, beacons, maps, or odometry.
The IMU is usually not the primary limit. Check corrections, antenna placement, multipath, convergence, and receiver configuration.
FREQUENTLY ASKED QUESTIONS
Dead reckoning propagates position, velocity, and attitude through a short complete blackout. It preserves a continuous state, not RTK accuracy; error grows until RTK Fixed or another reliable observation constrains it again.
In one KALMIX FIELD TEST, a 2.447 km tunnel segment reported 85.463% DR availability, CEP50 1.9 m, and R95 3.727 m. This is one measured pass, not a universal product specification; mounting, calibration, motion, temperature, and outage distance all matter.
Not always. GNSS + IMU describes the sensors present; GNSS/INS describes a system estimating a shared position, velocity, attitude, and error state. An integrated DR receiver and a tightly coupled estimator use those sensors differently.
Not always. Under sustained partial blockage, the receiver may remain in degraded Float rather than enter pure coasting, so an IMU may not recover a trustworthy absolute position. Test the GNSS state and blockage pattern, not only the scene name.
Usually not by itself. With healthy sky, RTK already supplies the absolute position; the IMU mainly adds continuity, attitude, or a higher-rate fused state.
No. The Kalmix evidence on this page was measured without wheel-speed input. Wheel speed can reduce vehicle-model drift, but its timestamp, direction, scale, tyre condition, and slip must be validated.
No. A single GNSS antenna normally reports course over ground while moving; dual antennas can observe a baseline orientation. An IMU propagates yaw from angular motion, but yaw drifts without motion or another absolute reference.
RTK/IMU fusion depends on short-term inertial propagation and trustworthy absolute updates. Because inertial error accumulates, RTK Fixed position and GNSS velocity constrain drift; Float or multipath-biased positions should not be treated as equal resets.
Not necessarily. An IMU can propagate a smooth fused state between GNSS updates, but first compare the GNSS solution rate and the fused navigation output rate. If continuity and attitude are unnecessary, native GNSS output may be simpler.
DEFINE THE OUTAGE FIRST
If you are evaluating a receiver or module with dead reckoning, share the outage type, acceptable exit error, RTK Fixed return point, vehicle or platform, mounting geometry, and any wheel-speed or external aids. Kalmix will recommend the simplest architecture that fits.
