determining angle of device with horizon as axis -android

Question

I have an interesting problem. I am trying to trace out the angle of a users phone regardless of whether they are holding it in landscape or portrait or any where in between..

I am currently using SENSOR_ORIENTATION and getting YAW, ROLL, and Pitch. I was also trying to get the angle of the users view port on the zaxis using yaw, and to correct for the users roll (landscape, portrait, or in between) i did some simple math..:

double roll = phoneOri.getRoll();
double yaw = phoneOri.getYaw()+roll;

     if (yaw>=360){
                yaw = (yaw - 360);
            }
            if (yaw<0){
                yaw = (yaw+360);    
            }

this code corrects the yaw and gives me the proper angle no matter what the roll position is..
but this sort of math doesn't correct for pitch it seems. if i hold my phone perpendicular to the floor i want to always get a pitch of 0 regardless of roll or yaw, if i face the back of the phone straight up to the sky and parallel to the ground i want to get 90, back to the ground -90;

here is how i am getting pitch roll and yaw:

    double yaw;
    double pitch;
    double roll;

public void onSensorChanged(SensorEvent evt) {
            int type=evt.sensor.getType();
            if(type == Sensor.TYPE_ORIENTATION){
                yaw = evt.values[0];
                pitch = evt.values[1];
                roll = evt.values[2];
            }
            if (type == Sensor.TYPE_MAGNETIC_FIELD) {
                orientation[0]=(orientation[0]*1+evt.values[0])*0.5f;
                orientation[1]=(orientation[1]*1+evt.values[1])*0.5f;
                orientation[2]=(orientation[2]*1+evt.values[2])*0.5f;
            } else if (type == Sensor.TYPE_ACCELEROMETER) {
                acceleration[0]=(acceleration[0]*2+evt.values[0])*0.33334f;
                acceleration[1]=(acceleration[1]*2+evt.values[1])*0.33334f;
                acceleration[2]=(acceleration[2]*2+evt.values[2])*0.33334f;
            }
            if ((type==Sensor.TYPE_MAGNETIC_FIELD) || (type==Sensor.TYPE_ACCELEROMETER)) {
                float newMat[]=new float[16];

                //Toast toast = Toast.makeText(ctx.getApplicationContext(), "accel", Toast.LENGTH_SHORT);
                //toast.show();
                SensorManager.getRotationMatrix(newMat, null, acceleration, orientation);
                if(displayOri==0||displayOri==2){
                    SensorManager.remapCoordinateSystem(newMat,SensorManager.AXIS_X*-1, SensorManager.AXIS_MINUS_Y*-1,newMat);
                }else{
                    SensorManager.remapCoordinateSystem(newMat,SensorManager.AXIS_Y, SensorManager.AXIS_MINUS_X,newMat);
                }

                matrix=newMat;
                SensorManager.getOrientation (newMat, orientationValues); 
            }
        }

currently i get the following results:

pitch = -90 roll = 0 ;

pitch = 0 roll = 90 ;

pitch = 90 roll = -20 ;

pitch = 0 roll = -90 ;

I am trying to get a pitch of 0 in any of these positions and then get a pitch between -90 and 90 respectively as the user tilts the phone on the HORIZON axis?

any ideas? oh and i should add that my application is locked to landscape mode..

Answer 1

Those constants probably have cumlative errors. Try using the Math functions instead...

Answer 2

Interesting problem,

have you tried getting the absolute x,y and z values (irrespective of the orientation of the phone) as mentioned here , using that, you should get the absolute y values that you are looking for

public abstract void onSensorChanged (int sensor, float[] values)

> IMPORTANT NOTE: The axis are swapped when the device's screen orientation changes. To access the unswapped values, use indices 3, 4 and 5 in values[].