使用重力傳感器
重力傳感器提供了三個維度的矢量,用來指示重力的方向和重量。下列代碼顯示了如何獲取一個默認的重力傳感器的實例:
private SensorManager mSensorManager;
private Sensor mSensor;
...
mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_GRAVITY);
單位與加速度傳感器所使用的單位(m/s2)相同,並且坐標系統也與加速度傳感器所使用的坐標系相同。
注意:當設備處於靜止狀態時,重力傳感器的輸出應該與加速度傳感器的輸出相同。
使用陀螺儀
陀螺儀以rad/s(弧度/每秒)为單位圍繞設備的X、Y、Z軸來測量速率或旋轉角度。下列代碼顯示了如何獲取一個默認的陀螺儀的實例:
private SensorManager mSensorManager;
private Sensor mSensor;
...
mSensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
mSensor = mSensorManager.getDefaultSensor(Sensor.TYPE_GYROSCOPE);
該傳感器的坐標系統與加速度傳感器所使用的坐標系統是相同的。逆時針方向旋轉是正值,也就是說,如果設備是逆時針旋轉,那麼觀察者就會看到一些有關以設備原點为中心的正向的X、Y、Z軸的位置。這是標准的正向旋轉的數學定義,並且與方向傳感器所使用的用於滾動的定義不同。
通常,陀螺儀的輸出會被集成到時間上,以便計算在一定時間不長之上旋轉角度的變化。例如:
// Create a constant to convert nanoseconds to seconds.
privatestaticfinalfloat NS2S =1.0f/1000000000.0f;
privatefinalfloat[] deltaRotationVector =newfloat[4]();
privatefloat timestamp;
publicvoid onSensorChanged(SensorEventevent){
// This timestep's delta rotation to be multiplied by the current rotation
// after computing it from the gyro sample data.
if(timestamp !=0){
finalfloat dT =(event.timestamp - timestamp)* NS2S;
// Axis of the rotation sample, not normalized yet.
float axisX =event.values[0];
float axisY =event.values[1];
float axisZ =event.values[2];
// Calculate the angular speed of the sample
float omegaMagnitude = sqrt(axisX*axisX + axisY*axisY + axisZ*axisZ);
// Normalize the rotation vector if it's big enough to get the axis
// (that is, EPSILON should represent your maximum allowable margin of error)
if(omegaMagnitude > EPSILON){
axisX /= omegaMagnitude;
axisY /= omegaMagnitude;
axisZ /= omegaMagnitude;
}
// Integrate around this axis with the angular speed by the timestep
// in order to get a delta rotation from this sample over the timestep
// We will convert this axis-angle representation of the delta rotation
// into a quaternion before turning it into the rotation matrix.
float thetaOverTwo = omegaMagnitude * dT /2.0f;
float sinThetaOverTwo = sin(thetaOverTwo);
float cosThetaOverTwo = cos(thetaOverTwo);
deltaRotationVector[0]= sinThetaOverTwo * axisX;
deltaRotationVector[1]= sinThetaOverTwo * axisY;
deltaRotationVector[2]= sinThetaOverTwo * axisZ;
deltaRotationVector[3]= cosThetaOverTwo;
}
timestamp =event.timestamp;
float[] deltaRotationMatrix =newfloat[9];
SensorManager.getRotationMatrixFromVector(deltaRotationMatrix, deltaRotationVector);
// User code should concatenate the delta rotation we computed with the current rotation
// in order to get the updated rotation.
// rotationCurrent = rotationCurrent * deltaRotationMatrix;
}
}
標准的陀螺儀提供了原始的旋轉數據,並不帶有任何過滤或噪音和漂移(偏心)的校正。在實踐中,陀螺儀的噪音和漂移會引入錯誤,因此需要對此進行抵消處理。通常通過監視其他傳感器,如重力傳感器或加速度傳感器來判斷漂移(偏心)和噪音。
From:CSDN
留言列表