Linker issue in opencv - visual-studio

Question

I am using OpenCV 2.4.6 in Visual Studio 2012 and I have testing one of the sample programs , name matcher_simple.cpp -- which matches two sample images , image1 and image2.
#include <stdio.h>
#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/nonfree/nonfree.hpp"
#include "opencv2/opencv.hpp"
using namespace cv;
static void help()
{
printf("\nThis program demonstrates using features2d detector, descriptor extractor and simple matcher\n"
"Using the SURF desriptor:\n"
"\n"
"Usage:\n matcher_simple <image1> <image2>\n");
}
int main(int argc, char** argv)
{
if(argc != 3)
{
help();
return -1;
}
//cv::initModule_nonfree();
Mat img1 = imread(argv[1], CV_LOAD_IMAGE_GRAYSCALE);
Mat img2 = imread(argv[2], CV_LOAD_IMAGE_GRAYSCALE);
if(img1.empty() || img2.empty())
{
printf("Can't read one of the images\n");
return -1;
}
// detecting keypoints
SurfFeatureDetector detector(400);
vector<KeyPoint> keypoints1, keypoints2;
detector.detect(img1, keypoints1);
detector.detect(img2, keypoints2);
// computing descriptors
SurfDescriptorExtractor extractor;
Mat descriptors1, descriptors2;
extractor.compute(img1, keypoints1, descriptors1);
extractor.compute(img2, keypoints2, descriptors2);
// matching descriptors
BFMatcher matcher(NORM_L2);
vector<DMatch> matches;
matcher.match(descriptors1, descriptors2, matches);
// drawing the results
namedWindow("matches", 1);
Mat img_matches;
drawMatches(img1, keypoints1, img2, keypoints2, matches, img_matches);
imshow("matches", img_matches);
waitKey(0);
return 0;
}
On compiling I get this error :
1>------ Build started: Project: opencvreinstated, Configuration: Release x64 ------
1>matcher_simple.obj : error LNK2001: unresolved external symbol "public: __cdecl cv::SURF::SURF(void)" (??0SURF#cv##QEAA#XZ)
1>matcher_simple.obj : error LNK2001: unresolved external symbol "public: __cdecl cv::SURF::SURF(double,int,int,bool,bool)" (??0SURF#cv##QEAA#NHH_N0#Z)
1>C:\Users\motiur\documents\visual studio 2012\Projects\opencvreinstated\x64\Release\opencvreinstated.exe : fatal error LNK1120: 2 unresolved externals
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
I have testing this in release mode 64 bit , I also have successfully ran simple other opencv samples , for example streaming live video . I did not have these sort of issues there . Help is appreciated . Thanks.

Answer 1

You have to link in the nonfree module, since this is where the Surf features are implemented.
Go to project Properties -> Linker -> Input, and add smth like opencv_nonfree246d.dll to Additional Dependencies field.
For details, please, see http://docs.opencv.org/doc/tutorials/introduction/windows_visual_studio_Opencv/windows_visual_studio_Opencv.html#the-local-method