使用RANSAC估计两组点之间的二维变换。

Question

据我所知，OpenCV使用RANSAC是为了解决这个问题。findHomography 并返回一些有用的参数，如 homograph_mask.

但是，如果我只想估计二维变换，也就是Affine Matrix，是否有办法使用同样的方法，即 findHomography 使用RANSAC并返回该掩码？

Answer 1

你可以直接使用 estimateAffinePartial2D 。https:/docs.opencv.org4.0.0d9d0cgroup__calib3d.html#gad767faff73e9cbd8b9d92b955b50062d。

cv::Mat cv::estimateAffinePartial2D (   
    InputArray  from,
    InputArray  to,
    OutputArray     inliers = noArray(),
    int     method = RANSAC,
    double  ransacReprojThreshold = 3,
    size_t  maxIters = 2000,
    double  confidence = 0.99,
    size_t  refineIters = 10 
)   

比如:

        src_pts = np.float32([pic1.key_points[m.queryIdx].pt for m in matches]).reshape(-1, 1, 2)
        dst_pts = np.float32([pic2.key_points[m.trainIdx].pt for m in matches]).reshape(-1, 1, 2)

        # Find the transformation between points, standard RANSAC
        transformation_matrix, mask = cv2.findHomography(src_pts, dst_pts, cv2.RANSAC, 5.0)

        # Compute a rigid transformation (without depth, only scale + rotation + translation) and RANSAC
        transformation_rigid_matrix, rigid_mask = cv2.estimateAffinePartial2D(src_pts, dst_pts)

Answer 2

估算刚性变形 内部确实使用了RANSAC，尽管目前参数是固定的--见这里的代码--。https:/github.comopencvopencvbmastermodulesvideosrclkpyramid.cpp。

cv::Mat cv::estimateRigidTransform( InputArray src1, InputArray src2, bool fullAffine )
{
    const int RANSAC_MAX_ITERS = 500;
    const int RANSAC_SIZE0 = 3;
    const double RANSAC_GOOD_RATIO = 0.5;

    // ...

    // RANSAC stuff:
    // 1. find the consensus
    for( k = 0; k < RANSAC_MAX_ITERS; k++ )
    {
        int idx[RANSAC_SIZE0];
        Point2f a[RANSAC_SIZE0];
        Point2f b[RANSAC_SIZE0];

        // choose random 3 non-complanar points from A & B
        for( i = 0; i < RANSAC_SIZE0; i++ )
        {
            for( k1 = 0; k1 < RANSAC_MAX_ITERS; k1++ )
            {