Euler angles are a representation of an angular frame, as are quaternions and rotation matrices.

Euler angles are a set of three angles, corresponding to pitch, roll, and yaw.

Euler angles may be constructed according to many conventions. The axes of and ordering of ordering of pitch, roll, and yaw vary by convention. The Embedded MotionApps Platform makes Euler angles available in the three most common conventions with MLGetEulerAnglesX, MLGetEulerAnglesY, and MLGetEulerAnglesZ. See the Embedded MotionApps Platform Functional Specification for specific details on the definition of these conventions.

Euler angles are not commutative. For any Euler angles A, B, a rotation A followed by B is not (B + A) is necessarily equal a rotation B followed by A (B + A). Because of this algebraic property, Euler angles are often not very useful for signal processing applications.

Euler angles suffer from a pair of singularity points at which only two of the three angles are significant. The derivative of the Euler angles is discontinuous at this point. This condition is often called gimbal lock.

Because 6 axis MotionFusion has no way to directly sense the earth’s magnetic field, it estimates heading by integrating the gyroscope sensor outputs. The gyroscope sensor will have some small amount of noise and may have small biases. Since the technique of gyroscope integration keeps a running sum of gyroscope sensor outputs and those sensor outputs include small errors, the sum will slowly accumulate an error over time. 6-axis MotionFusion can only correct part of this error using information from the accelerometer.

Both accelerometers and magnetometers are noisy sensors, which means they exhibit a slow response rate (due to noisy filtering) in fast moving systems. Accelerometer measurements are also affected by motion. By using a gyroscope and MotionFusion, the MotionFusion solution will have a faster response rate and track small, quick movements much more quickly. Gyroscope MotionFusion also makes it possible to sense linear acceleration separately from gravity.

Embedded MPL is the same as Embedded MotionApps Platform. It is the software solution for MotionProcessing from InvenSense, that is used with its production proven hardware such as IMU-3000, and MPU-6050, and MPU-9150. The intended applications for Embedded MotionApps Platform are microcontroller based, and expected to run in very small memory and processing footprints.

MotionProcessing is a term that collectively refers to 1) the integration of hardware sensors, such as the gyroscope, accelerometer, and compass 2) A computation engine for combining data from the individual sensors 3) Algorithms for calibration of sensor data.

The Embedded MotionApps Platform reference implementation for the Atmel UC3-A3 Xplained board takes 40k total program (ROM) memory and about 3K of data memory.
MotionFit SDK: 90kB
Motion Driver: 32kB total, 13kB for driver+DMP image

The Embedded MotionApps Platform provides MotionFusion of three axis gyroscope and three axis accelerometer data. The result is an angular frame which is relative to gravity (down). On its own, a three axis accelerometer can be used to find an angular frame relative to gravity. However, because accelerometers detect the sum of linear acceleration and gravity, an accelerometer cannot provide an accurate angular frame solution when it is in motion, which makes it unusable in many applications. By fusing the gyroscope with accelerometer, Embedded MotionApps delivers a stable angular frame solution which precisely follows the device motion.

With the Embedded MotionApps Platform, for 6-axis MotionFusion, ‘forward’, is the direction when the device initializes. Subsequent MotionFusion solutions will be described relative to this initial forwards direction.

9 axis MotionFusion combines gyroscope, accelerometer, and magnetometer sensor data. The resulting angular frame is relative to both gravity (down) and north. 9 axis MotionFusion is not available in Embedded MotionApps Platform at this time.

The advantages of 9 axis MotionFusion over 6 axis MotionFusion are that 9 axis MotionFusion results are usable for navigation and other applications which require information about the angle relative to north. It also eliminates any heading drift which may be present in a 6 axis MotionFusion solution.

Embedded MotionApps Platform provides a gyro bias tracker “ML_BIAS_FROM_NO_MOTION” which finds the gyro bias after an eight second period without motion.