Sensor transformation to world coordinate system
suggest changeThe sensor values returned by Android are with respective to the phone’s coordinate system (e.g. +Y points towards the top of the phone). We can transform these sensor values into a world coordinate system (e.g. +Y points towards magnetic North, tangential to the ground) using the sensor managers rotation matrix
First, you would need to declare and initialize the matrices/arrays where data will be stored (you can do this in the onCreate
method, for example):
float[] accelerometerData = new float[3];
float[] accelerometerWorldData = new float[3];
float[] gravityData = new float[3];
float[] magneticData = new float[3];
float[] rotationMatrix = new float[9];
Next, we need to detect changes in sensor values, store them into the corresponding arrays (if we want to use them later/elsewhere), then calculate the rotation matrix and resulting transformation into world coordinates:
public void onSensorChanged(SensorEvent event) {
sensor = event.sensor;
int i = sensor.getType();
if (i == Sensor.TYPE_ACCELEROMETER) {
accelerometerData = event.values;
} else if (i == Sensor.TYPE_GRAVITY) {
gravityData = event.values;
} else if (i == Sensor.TYPE_MAGNETIC) {
magneticData = event.values;
}
//Calculate rotation matrix from gravity and magnetic sensor data
SensorManager.getRotationMatrix(rotationMatrix, null, gravityData, magneticData);
//World coordinate system transformation for acceleration
accelerometerWorldData[0] = rotationMatrix[0] * accelerometerData[0] + rotationMatrix[1] * accelerometerData[1] + rotationMatrix[2] * accelerometerData[2];
accelerometerWorldData[1] = rotationMatrix[3] * accelerometerData[0] + rotationMatrix[4] * accelerometerData[1] + rotationMatrix[5] * accelerometerData[2];
accelerometerWorldData[2] = rotationMatrix[6] * accelerometerData[0] + rotationMatrix[7] * accelerometerData[1] + rotationMatrix[8] * accelerometerData[2];
}
Found a mistake? Have a question or improvement idea?
Let me know.
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