大虾：
       请教一下：如何使用三轴加速器 计算速度 与 方向
       android 7.1 
       我们使用的是 mpu6881 六轴的芯片，从android取的数据来看，只能取 Sensor.TYPE_ACCELEROMETER 的x y z 值
       我尝试这样取速度 ，速度没有变化
  public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
                long curTime = System.currentTimeMillis();
                double x = event.values[0];
                double y = event.values[1];
                double z = event.values[2];
                double xyz = (double)(x*x + y*y + z*z);

                yz_plane = (double)(Math.sqrt((y)*(y)+(z)*(z)));
                xz_plane = (double)(Math.sqrt((x)*(x)+(z)*(z)));
                xy_plane = (double)(Math.sqrt((x)*(x)+(y)*(y)));

                if(curTime-lastUpdate > TIME){
                    long diffTime = curTime-lastUpdate;
                    if(diffTime <= 0)diffTime = 1;
                    lastUpdate = curTime;
                    x = event.values[SensorManager.DATA_X];
                    y = event.values[SensorManager.DATA_X];
                    z = event.values[SensorManager.DATA_X];
                    double speed = Math.abs(x+y+z-last_x-last_y-last_z)/diffTime*10000;
                    Log.i("lock","  speed  "+speed);
                    if(speed > SHAKE_THRESHOLD){
                        Log.i("lock","speed = "+speed);
                        lastUpdate += 10000;//判断成功的话,10秒内不再判断
//                        handler.sendEmptyMessage(MessageID.MESSAGE_SENSOR);
                    }
                    last_x = x;
                    last_y = y;
                    last_z = z;
                }