指南针 ，导航
一般情况下，在android系统中获取手机的方位信息azimuth似乎是很简单的事情，在api中有TYPE_ORIENTATION常量，可以像得到加速度传感器那样得到方向传感器sm.getDefaultSensor(Sensor.TYPE_ORIENTATION)；然而，这一方法目前已不再使用。
其实，Android中的方向传感器也是是通过磁力计magnetometer和加速度传感器accelerometer抽象出来的。因此我们可以通过磁力计magnetometer和加速度传感器accelerometer来获得方位信息。由磁场和加速度如何得到方位信息的算法在api中已被封装好了。通过这种方式比直接获得方向传感器获得的信息更准确。
values[0] ：azimuth 方向角，但用（磁场+加速度）得到的数据范围是（-180～180）,也就是说，0表示正北，90表示正东，180/-180表示正南，-90表示正西。而直接通过方向感应器数据范围是（0～359）360/0表示正北，90表示正东，180表示正南，270表示正西。
values[1] pitch 倾斜角 即由静止状态开始，前后翻转
values[2] roll 旋转角 即由静止状态开始，左右翻转
//api中源码
public static float[] getOrientation(float[] R, float values[]) {
/*
* 4x4 (length=16) case:
* / R[ 0] R[ 1] R[ 2] 0 \
* | R[ 4] R[ 5] R[ 6] 0 |
* | R[ 8] R[ 9] R[10] 0 |
* \ 0 0 0 1 /
*
* 3x3 (length=9) case:
* / R[ 0] R[ 1] R[ 2] \
* | R[ 3] R[ 4] R[ 5] |
* \ R[ 6] R[ 7] R[ 8] /
*
*/
if (R.length == 9) {
values[0] = (float)Math.atan2(R[1], R[4]);
values[1] = (float)Math.asin(-R[7]);
values[2] = (float)Math.atan2(-R[6], R[8]);
} else {
values[0] = (float)Math.atan2(R[1], R[5]);
values[1] = (float)Math.asin(-R[9]);
values[2] = (float)Math.atan2(-R[8], R[10]);
}
return values;
}//getRotaionMatrix源码
public static boolean getRotationMatrix(float[] R, float[] I,
float[] gravity, float[] geomagnetic) {
// TODO: move this to native code for efficiency
float Ax = gravity[0];
float Ay = gravity[1];
float Az = gravity[2];
final float Ex = geomagnetic[0];
final float Ey = geomagnetic[1];
final float Ez = geomagnetic[2];
float Hx = Ey*Az - Ez*Ay;
float Hy = Ez*Ax - Ex*Az;
float Hz = Ex*Ay - Ey*Ax;
final float normH = (float)Math.sqrt(Hx*Hx + Hy*Hy + Hz*Hz);
if (normH < 0.1f) {
// device is close to free fall (or in space?), or close to
// magnetic north pole. Typical values are > 100.
return false;
}
final float invH = 1.0f / normH;
Hx *= invH;
Hy *= invH;
Hz *= invH;
final float invA = 1.0f / (float)Math.sqrt(Ax*Ax + Ay*Ay + Az*Az);
Ax *= invA;
Ay *= invA;
Az *= invA;
final float Mx = Ay*Hz - Az*Hy;
final float My = Az*Hx - Ax*Hz;
final float Mz = Ax*Hy - Ay*Hx;
if (R != null) {
if (R.length == 9) {
R[0] = Hx; R[1] = Hy; R[2] = Hz;
R[3] = Mx; R[4] = My; R[5] = Mz;
R[6] = Ax; R[7] = Ay; R[8] = Az;
} else if (R.length == 16) {
R[0] = Hx; R[1] = Hy; R[2] = Hz; R[3] = 0;
R[4] = Mx; R[5] = My; R[6] = Mz; R[7] = 0;
R[8] = Ax; R[9] = Ay; R[10] = Az; R[11] = 0;
R[12] = 0; R[13] = 0; R[14] = 0; R[15] = 1;
}
}
if (I != null) {
// compute the inclination matrix by projecting the geomagnetic
// vector onto the Z (gravity) and X (horizontal component
// of geomagnetic vector) axes.
final float invE = 1.0f / (float)Math.sqrt(Ex*Ex + Ey*Ey + Ez*Ez);
final float c = (Ex*Mx + Ey*My + Ez*Mz) * invE;
final float s = (Ex*Ax + Ey*Ay + Ez*Az) * invE;
if (I.length == 9) {
I[0] = 1; I[1] = 0; I[2] = 0;
I[3] = 0; I[4] = c; I[5] = s;
I[6] = 0; I[7] =-s; I[8] = c;
} else if (I.length == 16) {
I[0] = 1; I[1] = 0; I[2] = 0;
I[4] = 0; I[5] = c; I[6] = s;
I[8] = 0; I[9] =-s; I[10]= c;
I[3] = I[7] = I[11] = I[12] = I[13] = I[14] = 0;
I[15] = 1;
}
}
return true;
}
其中R[]数据是旋转数组，用来存放磁场和加速度的数据。之后在通过getOrientation方法通过一定的算法利用R[]得到方位信息values[]数组。
Code :
public class Orientation extends Activity implements
private SensorManager sm;
private ImageView orientation;
private Sensor aSensor;
private Sensor mSensor;
float[] accelerometerValues = new float[3];
float[] magneticFieldValues = new float[3];
float[] values = new float[3];
float[] rotate = new float[9];
@Override
protected void
// TODO
super.onCreate(savedInstanceState);
setContentView(R.layout.orientation);
orientation = (ImageView) findViewById(R.id.orientation);
orientation.setKeepScreenOn(true);
}
@Override
protected void
super.onResume();
sm = (SensorManager) this.getSystemService(SENSOR_SERVICE);
aSensor = sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
mSensor = sm.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
if (aSensor != null && mSensor != null) {
sm.registerListener(this, aSensor,
SensorManager.SENSOR_DELAY_NORMAL);
sm.registerListener(this, mSensor,
SensorManager.SENSOR_DELAY_NORMAL);
}
}
@Override
protected void
super.onPause();
sm.unregisterListener(this, aSensor);
sm.unregisterListener(this, mSensor);
}
private float predegree = 0;
@Override
public void
if (event.sensor.getType() == Sensor.TYPE_ACCELEROMETER) {
accelerometerValues = event.values;
}
if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {
magneticFieldValues = event.values;
}
SensorManager.getRotationMatrix(rotate, null, accelerometerValues,
magneticFieldValues);
/* 经过SensorManager.getOrientation(rotate, values);得到的values值为弧度 */
SensorManager.getOrientation(rotate, values);
/* 转换为角度 */
values[0] = (float) Math.toDegrees(values[0]);
float degree = values[0];
Log.i("jarlen", " degree = " + degree + " values[0] = " + values[0]);
if (Math.abs(degree + predegree) > 1) {
/** 动画效果 */
RotateAnimation animation = new RotateAnimation(predegree, degree,
Animation.RELATIVE_TO_SELF, 0.5f,
Animation.RELATIVE_TO_SELF, 0.5f);
animation.setDuration(200);
orientation.startAnimation(animation);
}
predegree
}
@Override
public void onAccuracyChanged(Sensor sensor, int
// TODO
}
}
