cvEstimateRigidTransform是opencv中求取仿射变换的函数，定义在lkpyramid.cpp文件中，该函数先利用ransac算法从所有特征点中选取一定数目的特征点，选取出的这些特征点性质都较好，然后利用icvGetRTMatrix函数求取仿射变换系数，下面是cvEstimateRigidTransform函数的详细注解。

CV_IMPL int
cvEstimateRigidTransform( const CvArr* matA, const CvArr* matB, CvMat* matM, int full_affine )
{
    const int COUNT = 15;
    const int WIDTH = 160, HEIGHT = 120;
    const int RANSAC_MAX_ITERS = 500;
    const int RANSAC_SIZE0 = 3;
    const double RANSAC_GOOD_RATIO = 0.5;

    cv::Ptr<CvMat> sA, sB; //智能指针，相当于c++中的shared_ptr
    cv::AutoBuffer<CvPoint2D32f> pA, pB;
    cv::AutoBuffer<int> good_idx;
    cv::AutoBuffer<char> status;
    cv::Ptr<CvMat> gray;

    CvMat stubA, *A = cvGetMat( matA, &stubA );  //将CvArr*类型的matA转化为CvMat类型的stubA，A是1*192
    CvMat stubB, *B = cvGetMat( matB, &stubB );
    CvSize sz0, sz1;
    int cn, equal_sizes;
    int i, j, k, k1;
    int count_x, count_y, count = 0;
    double scale = 1;
    CvRNG rng = cvRNG(-1);//初始化随机数发生器
    double m[6]={0};
    CvMat M = cvMat( 2, 3, CV_64F, m );
    int good_count = 0;
    CvRect brect;

    if( !CV_IS_MAT(matM) )
        CV_Error( matM ? CV_StsBadArg : CV_StsNullPtr, "Output parameter M is not a valid matrix" );

    if( !CV_ARE_SIZES_EQ( A, B ) )
        CV_Error( CV_StsUnmatchedSizes, "Both input images must have the same size" );

    if( !CV_ARE_TYPES_EQ( A, B ) )
        CV_Error( CV_StsUnmatchedFormats, "Both input images must have the same data type" );

    if( CV_MAT_TYPE(A->type) == CV_8UC1 || CV_MAT_TYPE(A->type) == CV_8UC3 )  //8位无符号
    {
        cn = CV_MAT_CN(A->type);  //返回通道数
        sz