Get where is facing the cellphone in android

Question

I'm trying to understand how can I know if the device's screen is facing the user or, for example, flat on a table with the screen looking up, or facing down, etc.

I'm not using the orientation sensor as it is deprecated I'm using the rotation matrix, I know pitch and roll values should be good the get that information, but before I get those values I need to remapcoordinatesystem and to know which Axle is the X and which one is the Y I need to know what is the screen facing.

For example: If the screen is facing the user I can use this mapping table

ROTATION_0      X   Y

ROTATION_90   -Y   X

ROTATION_180  -X  -Y

ROTATION_270  Y  -X

If the screen is facing the sky maybe I'll need to swap Y axle with Z axle, but I don't know how I can find out where is the screen facing.

Any ideas?

I'm also using this method I've find in the web (http://code.google.com/p/the-schwartz-unsheathed/source/browse/trunk/src/com/android/app/schwarz/PhoneOrientation.java?r=12)

 public static int getOrientation(float roll, float pitch) {
                int orientation = ORIENTATION_INVALID;

                if (Math.abs(roll) == 0.0 && Math.abs(pitch) == 0.0){
                    return ORIENTATION_INVALID;
                }

                if(roll >= -90 && roll <= -(90-mTolerance)){
                        orientation = ORIENTATION_FACE_LEFT;
                }
                else if(roll <= 90 && roll >= (90-mTolerance)){
                        orientation = ORIENTATION_FACE_RIGHT;
                    }

                if(pitch >= (90-mTolerance) && pitch <= (90+mTolerance)) {
                        if(orientation != ORIENTATION_INVALID){
                                orientation = ORIENTATION_INVALID;
                        }
                        else {
                                orientation = ORIENTATION_FACE_FORWARD;
                        }
                } else if(pitch <= -(90-mTolerance) && pitch >= -(90+mTolerance)) {
                        if(orientation != ORIENTATION_INVALID) {
                                orientation = ORIENTATION_INVALID;
                        }
                        else {
                                orientation = ORIENTATION_FACE_BACKWARD;
                        }
                }

                if((roll >= -mTolerance && roll <= mTolerance)) {
                        if((pitch >= -mTolerance && pitch <= mTolerance)) {
                                if(orientation != ORIENTATION_INVALID) {
                                        orientation = ORIENTATION_INVALID;
                                }
                                else {
                                        orientation = ORIENTATION_FACE_UP;
                                }
                        } else if((pitch <= -(180-mTolerance) && pitch >= -180) || (pitch >= (180-mTolerance) && pitch <= 180)) {
                                if(orientation != ORIENTATION_INVALID) {
                                        orientation = ORIENTATION_INVALID;
                                }
                                else {
                                        orientation = ORIENTATION_FACE_DOWN;
                                }
                        }
                }

                return orientation;
        }

Anyone has one better?

Answer 1

You can use Accelerometer, because it gives the x-y axis of the device, so you can get where the device is facing.