Essential Android SensorManager edit forum

Sensor transformation to world coordinate system

The 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];

}

Table Of Contents
39 ACRA
64 Menu
83 SensorManager
112 Loader
119 Xposed
132 Colors
135 Fresco
140 AdMob
147 Button
156 Vk SDK
170 XMPP
176 OpenCV
200 FileIO
203 Moshi
217 Paint
231 AIDL
241 JCodec
243 Okio
255 Looper
  ↑ ↓ to navigate     ↵ to select     Esc to close