正如我所看到的,在第三种方法中,您试图找到两个矢量(重力矢量和加速度矢量)之间角度的cos。这个想法是,如果角度接近于180度,那么如果角度接近0度,则表示您有向下移动。当角度从-90到90度时,余弦函数具有正值。所以当你的cosineVal
值是正值时,这意味着手机正在下降,即使余弦值接近1的运动是直线下降。所以反过来也是如此。当余弦为负值时(从90度到270度),你有运动。
可能你可以从Sensor.TYPE_ACCELEROMETER
从https://developer.android.com/reference/android/hardware/SensorEvent.html#values载荷那里你有重力矢量和加速度向量。
我在下面做了一段代码,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) {
}
}