matlab代码不能再使用VLFeat提供的任何函数。可以使用仿射变换通过RANSAC过滤嘈杂的SIFT匹配，输入：x1和x2是对应集（n×2矩阵）。ransac_thr和ransac_iter是RANSAC的误差阈值和迭代次数。 输出：3×3仿射变换。 仿射变换将x1变换为x2。可视化内点和变换后模板的边界以验证该结果蓝色：离群点；橙色：内点；红色：变换后模板的边界。

好的，下面是使用RANSAC和仿射变换实现SIFT匹配的Matlab代码，其中没有使用VLFeat提供的函数：

function [H, inliers] = sift_affine(x1, x2, ransac_thr, ransac_iter)

% SIFT matching using RANSAC with affine transformation

% Number of matches
n = size(x1, 1);

% Set maximum number of inliers and initialize affine transform
max_inliers = 0;
H = eye(3);

for i = 1:ransac_iter
    % Randomly select 3 pairs of points
    idx = randperm(n, 3);
    p1 = x1(idx, :);
    p2 = x2(idx, :);
    
    % Compute affine transform using selected points
    A = [p1(1,1) p1(1,2) 0 0 1 0; 0 0 p1(1,1) p1(1,2) 0 1;
         p1(2,1) p1(2,2) 0 0 1 0; 0 0 p1(2,1) p1(2,2) 0 1;
         p1(3,1) p1(3,2) 0 0 1 0; 0 0 p1(3,1) p1(3,2) 0 1];
    b = [p2(1,1); p2(1,2); p2(2,1); p2(2,2); p2(3,1); p2(3,2)];
    x = A \ b;
    Ht = [x(1) x(2) x(5); x(3) x(4) x(6); 0 0 1];
    
    % Compute error for each match
    err = zeros(n, 1);
    for j = 1:n
        p1j = [x1(j,1); x1(j,2); 1];
        p2j = [x2(j,1); x2(j,2); 1];
        e = p2j - Ht * p1j;
        err(j) = norm(e);
    end
    
    % Count inliers and update affine transform if necessary
    inliers_idx = find(err < ransac_thr);
    num_inliers = length(inliers_idx);
    if num_inliers > max_inliers
        max_inliers = num_inliers;
        inliers = inliers_idx;
        H = Ht;
    end
end

% Visualize inliers and transformed template boundaries
figure;
hold on;
scatter(x1(:,1), x1(:,2), 'b');
scatter(x2(:,1), x2(:,2), 'r');
scatter(x1(inliers,1), x1(inliers,2), 'o', 'MarkerFaceColor', 'orange');
scatter(x1(setdiff(1:n, inliers),1), x1(setdiff(1:n, inliers),2), 'x', 'MarkerEdgeColor', 'blue');
xlim([min([x1(:,1); x2(:,1)])-10 max([x1(:,1); x2(:,1)])+10]);
ylim([min([x1(:,2); x2(:,2)])-10 max([x1(:,2); x2(:,2)])+10]);
legend('Matched points', 'Transformed template', 'Inliers', 'Outliers');
title('SIFT matching with RANSAC and affine transformation');

% Compute bounding box of transformed template
w = size(template, 2);
h = size(template, 1);
corners = [1 1 1; w 1 1; w h 1; 1 h 1];
corners_trans = H * corners';
corners_trans = corners_trans ./ corners_trans(3,:);
bbox = [min(corners_trans(1,:)) min(corners_trans(2,:)) max(corners_trans(1,:)) max(corners_trans(2,:))];

% Visualize transformed template boundaries
figure;
imshow(template);
hold on;
plot([corners(:,1); corners(1,1)], [corners(:,2); corners(1,2)], 'b');
plot([corners_trans(:,1); corners_trans(1,1)], [corners_trans(:,2); corners_trans(1,2)], 'r');
xlim([bbox(1)-10 bbox(3)+10]);
ylim([bbox(2)-10 bbox(4)+10]);
legend('Template boundaries', 'Transformed template boundaries');
title('SIFT matching with RANSAC and affine transformation');

其中，x1和x2分别是匹配的两个点集（n×2矩阵），ransac_thr和ransac_iter分别是RANSAC的误差阈值和迭代次数。输出H是3×3仿射变换矩阵，将x1变换为x2。inliers是内点的索引向量，用于可视化内点和变换后模板的边界。