matlab-fuse-inertial-sensors

name	matlab-fuse-inertial-sensors
description	Analyzes sensor configurations and creates inertial fusion filters in MATLAB Navigation Toolbox. Manages filter selection (imufilter, ahrsfilter, complementaryFilter, insfilterMARG, insfilterAsync, insfilterNonholonomic, insfilterErrorState, insEKF, insCF), construction, tuning, and fusion loops. Use when fusing IMU/AHRS/INS/GPS+IMU data, estimating orientation or pose, or choosing a filter. Do NOT use for vision-only SLAM, Simulink fusion, or IMU simulation.
license	https://www.mathworks.com/content/dam/mathworks/license/pmrl/license.md
compatibility	R2022a+
metadata	{"author":"MathWorks","version":"1.1"}

When to Use

Select, implement, or tune an inertial sensor fusion filter in MATLAB Navigation Toolbox.

When NOT to Use

• Vision-only or LiDAR-only SLAM (no inertial sensor): use nav SLAM functions instead
• Sensor simulation or data generation only: no filter needed
• Simulink model-based sensor fusion

---

Choose Your Filter

Step 1 — Configured or Flexible?

Configured filters cover these sensor combinations exactly:

• Accel + Mag only (no gyro)
• Accel + Gyro (no mag, no GPS)
• Accel + Gyro + Mag
• Accel + Gyro + Mag + Altimeter
• Accel + Gyro + GPS (ground vehicle, no mag)
• Accel + Gyro + GPS + monocular visual odometry (ground vehicle)
• Accel + Gyro + Mag + GPS (synchronous rates)
• Accel + Gyro + Mag + GPS (mixed rates or dropped samples)

Is your sensor set one of the above?
        │ No ─────────────────────────────────────────────────────► Step 2B (Flexible)
        │ Yes
        ▼
Need a custom motion model (constant-velocity, bicycle, etc.)?
        │ Yes ────────────────────────────────────────────────────► Step 2B (Flexible)
        │ No
        ▼
Need RTS smoothing, StateCovariance output, or optimizer-based tune()?
        │ Yes ────────────────────────────────────────────────────► Step 2B (Flexible)
        │ No
        ▼
Batch-only processing (no real-time predict/fuse loop needed)?
        │ Yes ────────────────────────────────────────────────────► Step 2B (Flexible)
        │ No
        ▼
        Step 2A (Configured)

---

Step 2A — Pick a configured filter

What output do you need?
│
├─ Orientation only (no position)
│   │
│   ├─ Accel + Mag only (no gyro)
│   │   └──► ecompass   [function, not object; single-shot; useful for filter init]
│   │
│   ├─ Accel + Gyro (no mag)
│   │   └──► imufilter   [heading drifts over time without mag]
│   │
│   ├─ Accel + Gyro + Mag
│   │   ├──► ahrsfilter   [default; KF-based, statistically tunable]
│   │   └── lowest compute cost needed?
│   │       └──► complementaryFilter   [gain-based only; no KF, no tune()]
│   │
│   └─ Accel + Gyro + Mag + Altimeter
│       └──► ahrs10filter   [adds altitude + vertical velocity output]
│
└─ Full pose (orientation + position + velocity)
    │
    ├─ No motion constraints (aerial, or ground vehicle without side-slip constraint)
    │   ├─ Accel + Gyro + Mag + GPS, all sensors sync
    │   │   └──► insfilterMARG
    │   └─ Accel + Gyro + Mag + GPS, mixed rates or dropped samples
    │       └──► insfilterAsync
    │
    └─ Ground vehicle with zero side-slip constraint
        ├─ Accel + Gyro + GPS
        │   └──► insfilterNonholonomic
        └─ Accel + Gyro + GPS + monocular visual odometry
            └──► insfilterErrorState

---

Step 2B — Pick a flexible filter

Need real-time fusion, StateCovariance output, or optimizer-based tune()?
        │ Yes ──► insEKF   [production use; full KF; real-time and batch APIs]
        │ No
        ▼
Batch-only processing, no covariance needed, quick setup (R2026a+)?
        └──► insCF   [complementary filter; gain-based; not for production]

---

Data Preparation

Sample Rate

SampleRate (Group A filters) and IMUSampleRate (Group B filters) must match the actual data rate — a mismatch directly scales the noise model and corrupts all filter outputs. insfilterAsync, insEKF, and insCF are timestamp-driven and have no rate property.

Convert timestamps to seconds first, then infer the rate:

tSec = rawTimestamp / 1e6;   % µs → s; divide by 1e3 for ms, or skip if already seconds
fs = 1 / median(diff(tSec));

If timestamps are unusable (all identical, or non-finite result):

if numel(unique(tSec)) < 2 || ~isfinite(fs)
    fs = 100;   % use the stated or datasheet rate
end

Time Gaps

All stateful filters accumulate error across a recording gap (a large jump in timestamps). Split the data at each gap and reset the filter at the start of each segment.

gapThreshold = 5 / fs;                   % 5× the expected sample interval
gapIdx = find(diff(tSec) > gapThreshold);
segments = [1; gapIdx+1];                % start index of each segment

Group A System object filters (imufilter, ahrsfilter, complementaryFilter): call release(filt) between segments — resets state while preserving all tuned noise properties.

Group B and other filters: re-construct the filter object at the start of each segment.

---

Implementation

Consult the reference file for the filter you chose:

Filter group	Reference
Attitude filters	references/attitude-filters.md
Navigation filters	references/navigation-filters.md
insEKF	references/insekf.md
insCF	references/inscf.md

---

Tuning

Two tune signatures exist — mixing them up is a common error:

• Signature A (imufilter, ahrsfilter) — modifies filter in-place: tune(filt, sensorData, groundTruth)
• Signature B (ahrs10filter, insfilterMARG, insfilterAsync, insfilterNonholonomic, insfilterErrorState, insEKF) — returns noise struct: tunedNoise = tune(filt, tunernoise(filt), sensorData, groundTruth)

Not tunable via tune:

• ecompass, complementaryFilter — no tune method; adjust properties manually
• insCF — use gainparts(filt, sensorName, value) instead

insEKF only: tunerconfig requires a filter instance — tunerconfig(filt), not tunerconfig('insEKF')

tunerconfig

Property	Default	Description
MaxIterations	20	Stop after this many iterations
ObjectiveLimit	0.1	Stop when cost drops below this value
Display	"iter"	"iter" prints progress each iteration; "none" suppresses output
Cost	"RMS"	"RMS" minimizes RMS error; "Custom" uses CustomCostFcn
CustomCostFcn	[]	Function handle; active only when Cost = "Custom"

tunernoise Field Names by Filter

Signature B filters require tunernoise(filt) before calling tune. Signature A filters (imufilter, ahrsfilter) do not use tunernoise — tune modifies their noise properties directly in-place.

Filter	Fields returned by tunernoise
ahrs10filter	MagnetometerNoise, AltimeterNoise
insfilterMARG	MagnetometerNoise, GPSPositionNoise, GPSVelocityNoise
insfilterAsync	AccelerometerNoise, GyroscopeNoise, MagnetometerNoise, GPSPositionNoise, GPSVelocityNoise
insfilterNonholonomic	GPSPositionNoise, GPSVelocityNoise
insfilterErrorState	MVOOrientationNoise, MVOPositionNoise, GPSPositionNoise, GPSVelocityNoise
insEKF	Named by filt.SensorNames + Noise suffix (e.g. AccelerometerNoise, GPSNoise)

Fields use the ...Noise suffix — omitting it is a common mistake.

Visualizing Results

tunerPlotPose is an OutputFcn callback — pass it to tunerconfig to plot pose estimates live during each tuning iteration. It is not a standalone post-hoc plotting function; calling it directly with filter and data arguments will error ("Too many input arguments").

config = tunerconfig(filt);
config.OutputFcn = @tunerPlotPose;
tunedNoise = tune(filt, tunernoise(filt), sensorData, groundTruth, config);

For post-tuning visualization, extract the filter state and plot against your ground truth manually. Configured filters (ahrs10filter, insfilterMARG, insfilterAsync, insfilterNonholonomic, insfilterErrorState) have a pose() method — use it. insEKF and insCF have no pose() method — use stateparts(filt, 'Orientation'), stateparts(filt, 'Position'), etc. instead. For batch workflows, plot from the estimateStates output timetable.

For advanced patterns (controlling TunableParameters, custom cost functions, OutputFcn for logging/early stopping), see references/insekf.md and references/navigation-filters.md.

---

Conventions

• Reference frame: default is "NED". To use ENU:

  • Configured filter objects (imufilter, ahrsfilter, complementaryFilter, ahrs10filter, insfilterMARG, insfilterAsync, insfilterNonholonomic, insfilterErrorState): filt.ReferenceFrame = "ENU"
  • ecompass (a function, not an object): the orientationFormat positional arg is required before any name-value pairs — ecompass(a, m, 'quaternion', 'ReferenceFrame', 'ENU'). Omitting it errors: "Expected input number 3, FORMAT..."
  • insEKF/insCF: ReferenceFrame is read-only after construction; set via insOptions/insCFOptions at construction time

• Orientation output: quaternion object by default.

• GPS position input: LLA vector in degrees / degrees / meters.

• Sample rate property:

  • imufilter, ahrsfilter, complementaryFilter: SampleRate
  • ahrs10filter, insfilterMARG, insfilterNonholonomic, insfilterErrorState: IMUSampleRate
  • insfilterAsync, insEKF, insCF: no sample rate property (sensors carry their own timestamps)

• ReferenceLocation: must be set on insfilterMARG, insfilterAsync, insfilterNonholonomic, and insfilterErrorState before the fusion loop. For insEKF/insCF, set it on the insGPS/insCFGPS sensor object instead.

Skill Feedback

If this skill's guidance was wrong, incomplete, or didn't work, emit a plain-text feedback marker in your response, then continue with the task.

Format: NAV-SKILL-FEEDBACK [matlab-fuse-inertial-sensors] [category]: what failed; what you did instead Categories: wrong-command (incorrect/outdated), missing-guidance (omitted step), discovery-failure (suggested approach didn't work), platform-issue (environment-specific)

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