Android SensorManager getOrientation getRotationMatrix

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大家都知道Type_Orientation传感器已被遗弃，由加速度传感器和磁传感器借助一定的算法虚拟出方向来，利用SensorManager.getOrientation获取，其中一个参数就是R[]。这需要我们知道getRotationMatrix（）方法。

getRotationMatrix()方法说明中，定义的世界坐标系如下：

<img src="http://img.blog.csdn.net/20150802193335722" alt="" />

X轴平行于地面，指向东方。Y轴平行于地面，指向北极方向。Z轴垂直于地面，指向天空。

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;    }

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