Android Sensors for OpenGL

Question

I want to get the android sensors to work with opengl to rotate the opengl\'s camera to wherever the phone is pointing to.

To elaborate: if the player is looking at

Answer 1

You're supplying null for the inclination matrix - that's not correct.

SensorManager.getRotationMatrix(rotationMatrix, null, gravity, geomag);

There are lots of examples on how to use the SensorManager's getRotationMatrix(...).

float[] R = new float[16];
float[] I = new float[16];

if (SensorManager.getRotationMatrix(R, I, accelerometerValues, geomagneticValues)) {
    float[] anglesInRadians = new float[3];
    SensorManager.getOrientation(R, anglesInRadians);
    ...
}

Also "rotate the opengl's camera to wherever the phone is pointing to" is rather ambiguous. For instance, if you meant some sort of a augmented reality approach, then you should be mapping AXIS_X to AXIS_Z. Note that remapping might not even be necessary, e.g. when you already fix your activity to landscape mode. More details here.

Some example codes involving sensor data and OpenGL ES:

• CompassActivity
• How to use onSensorChanged sensor data in combination with OpenGL

Answer 2

Here is the way I did the same thing (my App was also in landscape). First I get the orientation values (similar to the way you do):

final float pi = (float) Math.PI;
final float rad2deg = 180/pi;
public static float x; //pitch
public static float y; //roll
public static float z; //azimuth    
float[] gravity = new float[3];
float[] geomag = new float[3];
float[] inOrientMatrix = new float[16];
float[] outOrientMatrix= new float[16];
float orientation[] = new float[3]; 
public static GLSurfaceView glView;

//  (...)

public void onSensorChanged(SensorEvent event) {
switch (event.sensor.getType()){  
        case Sensor.TYPE_ACCELEROMETER:  gravity = event.values.clone();
        break;
        case Sensor.TYPE_MAGNETIC_FIELD: geomag = event.values.clone();
        break;
        }
if (gravity != null && geomag != null){
if (SensorManager.getRotationMatrix(inOrientMatrix, null, gravity, geomag)){
        SensorManager.remapCoordinateSystem(inOrientMatrix, SensorManager.AXIS_X, SensorManager.AXIS_Z, outOrientMatrix);
        SensorManager.getOrientation(outOrientMatrix, orientation);
        x = orientation[1]*rad2deg; //pitch
        y = orientation[0]*rad2deg; //azimuth
        z = orientation[2]*rad2deg; //roll
        glView.requestRender();
｝

Then in my rendered, in the onDrawFrame(GL10 gl) I do:

 gl.glLoadIdentity();
 GLU.gluLookAt(gl, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, -1.0f, 0.0f, 1.0f, 0.0f);      
 gl.glRotatef(MainActivity.x, 1.0f, 0.0f, 0.0f);
 gl.glRotatef(MainActivity.y, 0.0f, 1.0f, 0.0f);
 gl.glRotatef(MainActivity.z, 0.0f, 0.0f, 1.0f);
 //in case you have transformation, eg. the position of the object, you can do them here 
 //gl.Translatef(0.0f, 0.0f, -DISTANCE NORTH); 
 //gl.Translatef(0.0f, DISTANCE EAST, 0.0f); 
 gl.glPushMatrix();
 //object draw

In other words, I rotate the whole world around me. A better way would be to change the direction of the camera using glLookAt, with the eye positioned at (0,0,0) and (0,1,0) being the up vector, but I simply couldn't get my center_view x,y,z values correctly.

Hope this helps...