QT + OpenCV undefiend reference to cv::stereoBM::create(int,int) - qt

Question

I need your help for a problem in OpenCV cv::StereoBM because I got an error when I tried bo compile the code below:
std::string myImgLeftString = myImgLeft.toUtf8().constData();
std::string myImgRightString = myImgRight.toUtf8().constData();
cv::Mat img1 = cv::imread(myImgLeftString,CV_LOAD_IMAGE_COLOR);
cv::Mat img2 = cv::imread(myImgRightString,CV_LOAD_IMAGE_COLOR);
cv::Mat img3;
cv::Mat img1grey, img2grey;
cv::cvtColor(img1,img1grey,CV_BGR2GRAY);
cv::cvtColor(img2,img2grey,CV_BGR2GRAY);
cv::Ptr<cv::StereoBM> match = cv::StereoBM::create(0,21);
match->compute(img1grey,img2grey,img3);
It gives me : undefiend reference to cv::StereoBM::create(int,int)
But I already include all the headers necessary and not necessary
#include <opencv2/core.hpp>
#include <opencv2/opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/calib3d.hpp>
#include <opencv2/imgproc.hpp>
#include <stdio.h>
#include <iostream>
#include <opencv2/core/affine.hpp>
#include "opencv2/core/hal/intrin.hpp"
#include "opencv2/core/utility.hpp"
#include "opencv2/ximgproc.hpp"
And I've added two lignes of code in my .pro file
LIBS += -L ./opt/local/lib -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs
INCLUDEPATH += -I /opt/local/stow/opencv-3.4.3
I don't know what is wrong, please kindly help, thanks.

Answer 1

cv::StereoBM is in calib3d module of OpenCV, so you need to link to the lib file of that module, to do that add -lopencv_calib3d to the LIBS in your .pro file:
LIBS += -L ./opt/local/lib -lopencv_core -lopencv_highgui -lopencv_imgproc -lopencv_imgcodecs -lopencv_calib3d
Don't forget to run qmake after you modify your .pro file.