【實用工具app】Cardan Linear Acceleration|最夯免費app-綠色工廠好玩App

Cardan Linear Acceleration provides an open source working code example and Android application that demonstrates how to calculate the gravity components of the acceleration sensor from the vector provided by SensorManager.getOrientation(). Cardan Linear Acceleration relies on the magnetic and acceleration sensors to determine the orientation of the device. The gravity component of the acceleration can be calculated from the acceleration sensor and subtracted from the signal to estimate linear acceleration.

This is not so much a example of how to calculate linear acceleration with SensorManager.getOrientation() as it is an example of how not to do it and why you need to be careful using Android sensors like LINEAR_ACCELERATION and ROTATION_VECTOR on devices that do not have a gyroscope. The jist of the algorithm itself can also be applied to a gyroscope, or other methods of determining orientation, with good results. This makes it a good basis for understanding how sensors fusions can be implemented, however, this specific implementation should only be used for learning purposes.

There are some limitations to the magnetic sensor which make this algorithm, overall, a poor choice in determining linear acceleration. An accelerometer alone will tell you pitch and roll; not yaw because gravity is parallel to yaw (z) and a magnetometer alone will tell you roll and yaw; not pitch because the Earth’s magnetic field is parallel to pitch (x). Note that the earth’s magnetic field is only horizontal to the earth’s surface at the equator. In North America and UK the earth’s magnetic field may be between 50 to 70 degrees to the horizontal. As a result, pitch, roll and yaw will all be erroneous. The orientation may only be considered correct around the 2 perpendicular rotational axis that are orthogonal to the true direction of the Earth’s magnetic field. Thus, the magnetic sensor cannot be used to determine the pitch and roll of the device, only the yaw, and we will not use the yaw to perform any of our calculations. It is only because the Android API requires both the magnetic and acceleration sensor to determine the orientation that the magnetic sensor is used (which is still a sensor fusion), but we will only use the accelerometer to determine the the gravity components of the acceleration of the device. There are more simple methods of doing this, one of which is discussed in Simple Linear Acceleration. However, this example does give an explanation of the coordinate systems used, and demonstrates how to determine the gravity components of the acceleration once the orientation of the device is known.

There are further limitations to the acceleration sensor. An acceleration sensor can only measure static tilt or dynamic acceleration, but not both at the same time. This means that if the pitch or roll of the acceleration sensor is changing, there is no way to accuratly measure linear acceleration. It is also impossible, in general, to measure angular displacement, velocity and acceleration with the acceleration sensor without another sensor to measure the orientation of the acceleration sensor. There are some exceptions to this. A low-pass filter, for example, can help to estimate linear acceleration unders some conditions, for example. However, for many applications, a gyroscope, acceleration and magnetic sensor are required.