Back end Method/technique behind the cvEstimateRigidTransform() function

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Hello Everyone,

I Want to know what technique is implemented behind the "cvEstimateRigidTransform()" opencv function. As I know that if I have to do it manually first I have to compute the feature points in both the Images and then gave the function corresponding points, So My question is which technique it is using for feature detection and corresponding pairs finding in order to get affine parameters ? As I used it for image rectification it is working fine. Now I want to try the rectification without using opencv that's why asking the method behind this function.

     Mat img_refernce = imread( pathOne, CV_LOAD_IMAGE_GRAYSCALE );
     Mat img_test = imread( pathTwo, CV_LOAD_IMAGE_GRAYSCALE );
     cv::Mat transformMat = cv::estimateRigidTransform(img_refernce, img_test ,true);

Thanks in advance