Question

我正在尝试使用Android设备上的加速计（Sensor.TYPE_LINEAR_ACCELERATION）计算位移。这是我的OnSensorChanged()方法：

public void onSensorChanged(SensorEvent event) {
    accelX = event.values[0];
    accelY = event.values[1];
    accelZ = event.values[2];

    long currentTime = System.currentTimeMillis() / 1000;

    if(prevTime == 0) prevTime = currentTime;

    long interval = currentTime - prevTime;
    prevTime = currentTime;     

    velX += accelX * interval;
    velY += accelY * interval;
    velZ += accelZ * interval;

    distX += prevVelX + velX * interval;
    distY += prevVelY + velY * interval;
    distZ += prevVelZ + velZ * interval;

    prevAccelX = accelX;        
    prevAccelY = accelY;        
    prevAccelZ = accelZ;

    prevVelX = velX;
    prevVelY = velY;
    prevVelZ = velZ;
}

然而，在任何移动后，Velocity都不会返回0。除非非常突然，否则减速效果不大。这导致一些非常不准确的距离值。

加速度计也非常嘈杂，所以我补充说：

accelX = (accelX * accelKFactor) + prevAccelX * (1 - accelKFactor);
accelY = (accelY * accelKFactor) + prevAccelY * (1 - accelKFactor);
accelY = (accelX * accelKFactor) + prevAccelY * (1 - accelKFactor);

accelKFactor = .01

我错过了一些明显的东西吗？

我的最终目标只是能够判断设备是否移动了超过10英尺，但是现在，我的数据几乎没用。

编辑：

我发现了部分问题。 currentTime很长，但我将系统时间以ms为单位除以1000得到秒。所以速度只能真正更新每1秒。将currentTime更改为双倍会有所帮助，但并不能完全解决问题。

Answer 1

SensorEvent有一个时间戳字段，以纳秒为单位。使用它而不是System.currentTimeMillis（）。以下是文档中的示例：

private static final float NS2S = 1.0f / 1000000000.0f;
 private float timestamp;

 public void onSensorChanged(SensorEvent event) {
      // This timestep's delta rotation to be multiplied by the current rotation
      // after computing it from the gyro sample data.
      if (timestamp != 0) {
          final float dT = (event.timestamp - timestamp) * NS2S;

通过这种方式跟踪位移对初始条件非常敏感，因此这应该有所帮助。

另外，您可能会更好地使用Location.getSpeed（）。如果您无法获得信号，请考虑仅将加速度计用作备份。

Answer 2

请检查下面的代码

public class MainActivity extends Activity implements SensorEventListener {
    private SensorManager sensorManager;
    float appliedAcceleration = 0;
    float currentAcceleration = 0;
    float velocity = 0;
    Date lastUpdatedate;
    double calibration = Double.NaN;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
                WindowManager.LayoutParams.FLAG_FULLSCREEN);

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        lastUpdatedate = new Date(System.currentTimeMillis());
        sensorManager = (SensorManager) getSystemService(SENSOR_SERVICE);
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        double x = event.values[0];
        double y = event.values[1];
        double z = event.values[2];
        double a = Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2) + Math.pow(z, 2));
        if (calibration == Double.NaN)
            calibration = a;
        else {
            Date timeNow = new Date(System.currentTimeMillis());
            long timeDelta = timeNow.getTime()-lastUpdatedate.getTime();
            lastUpdatedate.setTime(timeNow.getTime());
            float deltaVelocity = appliedAcceleration * (timeDelta/1000);
            appliedAcceleration = currentAcceleration;
            velocity += deltaVelocity;
            final double mph = (Math.round(100*velocity / 1.6 * 3.6))/100;
            Log.i("SensorTestActivity","SPEEDDDDD=== "+mph+"     "+velocity);
            currentAcceleration = (float)a;
        }
    }

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

    }

    @Override
    protected void onStart() {
        super.onStart();
        sensorManager.registerListener(this,
                sensorManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER),
                SensorManager.SENSOR_DELAY_NORMAL);
    }

    @Override
    protected void onStop() {
        super.onStop();
        sensorManager.unregisterListener(this);
    }
}

集成Android Accelerometer以查找速度和位置

2 个答案: