android – 线性加速方向,用于跟踪手机的上下移动

dotProduct = vectorA[0]*vectorB[0]+vectorA[1]*vectorB[1] + vectorA[2]*vectorB[2];    
cosineVal = dotProduct/(|vectorA|*|vectorB|)    
if(cosineVal > 0 ) down else Up.

在我看来,在第3种方法中,你试图找到两个矢量之间的角度cos(重力矢量和加速度矢量).并且想法是如果角度接近180度你有向上运动,如果角度接近0度你有向下运动.余弦是角度为-90到90度时具有正值的函数.因此,当你的cosineVal值为正时,这意味着手机正在下降,即使cosineVal接近1运动也是直线下降.所以反之亦然.当余弦为负时(从90度到270度),你就有了运动.

也许你可以从https://developer.android.com/reference/android/hardware/SensorEvent.html#values获得Sensor.TYPE_ACCELEROMETER的矢量,你有重力矢量和加速度矢量.
我在下面制作了一个代码片段,你可以试试.

public class MainActivity extends AppCompatActivity implements SensorEventListener {
    private float[] gravity = new float[3];
    private float[] linear_acceleration = new float[3];

    @Override
    protected void onCreate(Bundle savedInstanceStatE) {
        super.onCreate(savedInstanceStatE);
        setContentView(R.layout.activity_main);
        SensoRMANager mSensoRMANager = (SensoRMANager) getSystemservice(SENSOR_serviCE);
        Sensor mAccelerometer = mSensoRMANager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
        mSensoRMANager.registerListener(this,mAccelerometer,SensoRMANager.SENSOR_DELAY_NORMAL);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        // alpha is calculated as t / (t + dT)
        // with t,the low-pass filter's time-constant
        // and dT,the event delivery rate

        final float alpha = 0.8f;

        gravity[0] = alpha * gravity[0] + (1 - alpha) * event.values[0];
        gravitY[1] = alpha * gravitY[1] + (1 - alpha) * event.values[1];
        gravitY[2] = alpha * gravitY[2] + (1 - alpha) * event.values[2];

        linear_acceleration[0] = event.values[0] - gravity[0];
        linear_acceleration[1] = event.values[1] - gravitY[1];
        linear_acceleration[2] = event.values[2] - gravitY[2];

        float scalarProduct = gravity[0] * linear_acceleration[0] +
                gravitY[1] * linear_acceleration[1] +
                gravitY[2] * linear_acceleration[2];
        float gravityVectorLength = (float) Math.sqrt(gravity[0] * gravity[0] +
                gravitY[1] * gravitY[1] + gravitY[2] * gravitY[2]);
        float lianearAccVectorLength = (float) Math.sqrt(linear_acceleration[0] * linear_acceleration[0] +
                linear_acceleration[1] * linear_acceleration[1] + linear_acceleration[2] * linear_acceleration[2]);

        float cosVectorAngle = scalarProduct / (gravityVectorLength * lianearAccVectorLength);

        TextView tv = (TextView) findViewById(R.id.tv);
        if (lianearAccVectorLength > 2) {//increase to detect only bigger accelerations,decrease to make detection more sensitive but noisy
            if (cosVectorAngle > 0.5) {
                tv.setText("Down");
            } else if (cosVectorAngle < -0.5) {
                tv.setText("Up");
            }
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor,int i) {

    }
}