IMU

The M1 streams IMU samples alongside video on the same transport. retrieve_imu() drains the queued samples in chronological order after a successful grab(). At typical rates, a frame interval contains several IMU samples. Leave InitParameters::enable_imu enabled, then use a USB or WiFi/UDP data plane. A control-only Bluetooth LE (BLE) session cannot deliver IMU samples.

SensorsData sensors;
while (dev.grab() == ERROR_CODE::SUCCESS) {
    if (dev.retrieve_imu(sensors) != ERROR_CODE::SUCCESS) continue;

    for (const ImuSample& s : sensors.samples) {
        // s.acceleration[3]      m/s^2
        // s.angular_velocity[3]  rad/s
        // s.temperature_c        die temperature
        // s.timestamp            device clock, ns
        // s.sequence             monotonic; gaps = wire loss
    }
    if (sensors.motion_state == MOTION_STATE::FALLING) {
        // free-fall detected
    }
}

SensorsData

Field	Meaning
`samples`	every `ImuSample` since the last drain, in order
`dropped`	ring-overrun count (host consumed too slowly)
`motion_state`	`STATIC` / `MOVING` / `FALLING`, classified by the host SDK from the newest sample

Timestamps and ordering

Sample timestamps are on the device clock, the same timebase as Mat::getTimestamp(), so associating IMU windows to frames is a direct comparison. sequence increments per sample; a gap means samples were lost in transit (lossy UDP) or overrun (dropped). retrieve_imu(data, TIME_REFERENCE::IMAGE) is the default and returns the queued batch aligned to the grabbed frame. Samples arriving between calls queue for the next drain. Passing TIME_REFERENCE::CURRENT keeps only the newest available sample. flip_mode and coordinate_system are applied when samples are delivered. Recordings preserve the raw IMAGE-frame data.

Sensor configuration

Noise densities and the camera↔IMU extrinsic transform ship on the device and are cached at open():

SensorsConfiguration sc = dev.get_device_information().sensors_configuration;
// sc.accelerometer.sampling_rate   Hz
// sc.accelerometer.range           +/- g (accel) or +/- deg/s (gyro)
// sc.accelerometer.noise_density
// sc.gyroscope.noise_density
// sc.camera_imu_transform          4x4, camera frame -> IMU frame

Read the rate from sampling_rate rather than assuming one. The block also carries the stored field calibration (accel_bias, gyro_bias, the two 3×3 scale-misalignment matrices, and time_offset_ns), which is what Calibration writes.

Disable the IMU with InitParameters::enable_imu = false when only video is required. This removes the IMU packets from the wire entirely.

Getting Started

Device

Command-Line Tools

SensorsData

Timestamps and ordering

Sensor configuration

​SensorsData

​Timestamps and ordering

​Sensor configuration

SensorsData

Timestamps and ordering

Sensor configuration