Running cv::warpPerspective on points

Question

I'm running the cv::warpPerspective() function on a image and what to get the position of the some points of result image the I get in the source image, here how far I came :

 int main (){
    cv::Point2f srcQuad[4],dstQuad[4];
    cv::Mat warpMatrix;
    cv::Mat src, dst,src2;
    src = cv::imread("card.jpg",1);
            srcQuad[0].x = 0; //src Top left
    srcQuad[0].y = 0;
    srcQuad[1].x = src.cols - 1; //src Top right
    srcQuad[1].y = 0;
    srcQuad[2].x = 0; //src Bottom left
    srcQuad[2].y = src.rows - 1;
    srcQuad[3].x = src.cols -1; //src Bot right
    srcQuad[3].y = src.rows - 1;
    dstQuad[0].x = src.cols*0.05; //dst Top left
    dstQuad[0].y = src.rows*0.33;
    dstQuad[1].x = src.cols*0.9; //dst Top right
    dstQuad[1].y = src.rows*0.25;
    dstQuad[2].x = src.cols*0.2; //dst Bottom left
    dstQuad[2].y = src.rows*0.7;
    dstQuad[3].x = src.cols*0.8; //dst Bot right
    dstQuad[3].y = src.rows*0.9;

    warpMatrix =cv::getPerspectiveTransform(srcQuad,dstQuad);

    cv::warpPerspective(src,dst,warpMatrix,src.size());
    cv::imshow("source", src);
    cv::imshow("destination", dst);
    cv::warpPerspective(dst,src2,warpMatrix,dst.size(),CV_WARP_INVERSE_MAP);
    cv::imshow("srouce 2 " , src2);
    cv::waitKey();
    return 0;

my problem is that if I select a point from dst how can get its coordinates in ** src or src2 ** since the cv::warpPerspective function doesn't take cv::Point as parameter ??

Answer 1

You want perspectiveTransform (which works on a vector of Points) rather than warpPerspective. Take the inverse of warpMatrix; you may have to tweak the final column.

vector<Point2f> dstPoints, srcPoints;
dstPoints.push_back(Point2f(1,1));

cv::perspectiveTransform(dstPoints,srcPoints,warpMatrix.inv());