Quaternion_Pitch.swift

    /**
    Calculates the pitch angle for the device based on it's orientation from the Quaternion
    
    - parameter quat: The Quaternary from CMMotionManager.attitude
    
    - returns: pitch The pitch of the device, scaled so that vertical is 0 degrees
    */
    private func pitchFromQuaternion(quat: CMQuaternion) -> Double {
        // http://stackoverflow.com/questions/9478630/get-pitch-yaw-roll-from-a-cmrotationmatrix/18764368#18764368
        //let degRoll = radiansToDegrees(atan2(2*(quat.y*quat.w - quat.x*quat.z), 1 - 2*quat.y*quat.y - 2*quat.z*quat.z))
        let degPitch = radiansToDegrees(atan2(2*(quat.x*quat.w + quat.y*quat.z), 1 - 2*quat.x*quat.x - 2*quat.z*quat.z))
        let degYaw = radiansToDegrees(asin(2*quat.x*quat.y + 2*quat.w*quat.z))
        
        var correctPitch = degPitch - 90.0 //Scale so that vertical is 0 (default is 90)
        if orientation != nil {
            switch orientation! {
            case .Portrait:
                break
            case .PortraitUpsideDown:
                correctPitch = -degPitch - 90.0
                break
            case .LandscapeLeft:
                correctPitch = degYaw
                break
            case .LandscapeRight:
                correctPitch = -degYaw
                break
            default:
                break
            }
        }
        
        return correctPitch
    }