转载：根据5个人脸特征点，快速计算人脸角度

转载：https://blog.csdn.net/minus/article/details/120020027
精准详细的计算可以参考：https://blog.csdn.net/u014090429/article/details/100762308
// 计算翻滚角
float getRoll(int leftEyeX, int leftEyeY, int rightEyeX, int rightEyeY)
{
    float dx = rightEyeX - leftEyeX;
    float dy = rightEyeY - leftEyeY;
    
    if (fabs(dx) < 0.0000001f)
        return 0.f;
    else
        return atanf(dx / dy)*180.0f / 3.1415926;    
}
 
// 计算水平角
float getYaw(int noseX, int faceX, int faceWidth)
{
    float dx = noseX - faceX;
    float rate = dx / (faceWidth * 0.5f) - 1;
    return asinf(rate)*180/3.1415926; 
}
 
// 计算俯仰角
float getPitch(int noseY, int faceY, int faceHigh)
{
    float dy = noseY - faceY;
    float rate = dy / (faceHigh*0.6f) - 1;
    return asinf(rate)*180/3.1415926;
}