Android: IMU data

The sample

Each motion sample carries:

Field	Unit
timestampNs	Nanoseconds on the camera clock (the same clock as the frame timestamps)
accel	m/s², x/y/z, gravity included
gyro	rad/s, x/y/z
mag	µT, x/y/z — live on cameras with a magnetometer
tempC	Sensor temperature, °C

The trailing per-sample value means different things by generation (a frame-sync delay on V1/V2, the magnetometer reading's age on newer cameras); use SeiImuParser.deriveSofNs(sample, version) rather than interpreting it yourself.

Rate

400 Hz on current cameras, about 562 Hz on V1/V2. Each video frame carries the samples captured since the previous frame — about 13 per frame at 400 Hz. Read the rate from the data rather than assuming it.

Live samples from the stream

session.frames
    .onEach { frame ->
        for (payload in SeiImuParser.parse(frame.annexB)) {
            // payload.header: version, sample count, sensor ranges
            for (sample in payload.samples) {
                // sample.timestampNs, sample.accel, sample.gyro, sample.mag, …
            }
        }
    }
    .launchIn(scope)

Orientation (Madgwick fusion)

val madgwick = Madgwick(beta = 0.1f)
var lastNs = 0L

fun onSample(s: ImuSample) {
    if (lastNs == 0L) {
        madgwick.seedFromAccel(s.accel[0], s.accel[1], s.accel[2])
    } else {
        val dt = (s.timestampNs - lastNs).coerceAtLeast(0L) / 1e9f
        madgwick.updateIMU(s.gyro[0], s.gyro[1], s.gyro[2], s.accel[0], s.accel[1], s.accel[2], dt)
    }
    lastNs = s.timestampNs
    val quatXyzw = madgwick.asXyzw()
}

UI widgets (Compose)

ImuOverlayPanel (live values), OrientationCube (quaternion-driven 3D cube) and TimeSeriesPlot / TripleAxisPlot (scrolling plots).

For aligning samples to frames, see Timing and sync. More: IMU guide on GitHub.