IMU Data Format

IMU Data

For detailed field descriptions, see IMUFrame Properties in API Reference.

IMU Coordinate System

Coordinate Frame (iPhone device frame):

• X-axis: Right (when holding phone in portrait)

• Y-axis: Up (toward top of device)

• Z-axis: Forward (out of screen)

IMU Data Explained

The IMU data follows Apple's CoreMotion framework conventions. For comprehensive details, refer to Apple's CoreMotion Documentation.

Accelerometer

Total acceleration measured by the device's accelerometer hardware.

• Unit: G (gravitational force units, where $1G = 9.81 \text{ m/s}^2$)

Gyroscope

Angular velocity around each axis.

• Unit: rad/s (radians per second)

Magnetometer

Magnetic field strength detected by the device.

• Unit: μT (microteslas)

Gravity Vector

Component of acceleration due to Earth's gravitational pull, isolated from user motion.

• Unit: G (gravitational force units)

• Magnitude: $|\vec{g}| \approx 1.0G$ when stationary

• Usage: Determining device orientation relative to Earth

• Reference: CMDeviceMotion.gravity

User Acceleration

Acceleration from user motion, with gravity removed.

• Unit: G (gravitational force units)

• Formula: $\vec{a}_{user} = \vec{a}_{total} - \vec{g}$

• Reference: CMDeviceMotion.userAcceleration

Attitude (Quaternion)

Device orientation in 3D space.

• Format: $[q_x, q_y, q_z, q_w]$ (quaternion)

• Reference: CMAttitude