Question

I am trying to compile a sample openCV project which uses SURF for image matching.

The code is listed bellow :

#include <stdio.h>
#include <iostream>
#include <cv.h>
#include <cxcore.h>
#include <highgui.h>
//#include "opencv2/core/core.hpp"
//#include "opencv2/features2d/features2d.hpp"
//#include "opencv2/highgui/highgui.hpp"

using namespace cv;

void readme();

/** @function main */
int main()
{
/*
if( argc != 3 )
{ readme(); return -1; }

Mat img_1 = imread( argv[1], CV_LOAD_IMAGE_GRAYSCALE );
Mat img_2 = imread( argv[2], CV_LOAD_IMAGE_GRAYSCALE );
*/

Mat img_1 = imread("D:\\A.jpg", CV_LOAD_IMAGE_GRAYSCALE);
Mat img_2 = imread("D:\\backImg.jpg", CV_LOAD_IMAGE_GRAYSCALE);

if( !img_1.data || !img_2.data )
{ std::cout<< " --(!) Error reading images " << std::endl; return -1; }

//-- Step 1: Detect the keypoints using SURF Detector
int minHessian = 400;

SurfFeatureDetector detector;

std::vector<KeyPoint> keypoints_1, keypoints_2;

detector.detect( img_1, keypoints_1 );
detector.detect( img_2, keypoints_2 );

//-- Step 2: Calculate descriptors (feature vectors)
SurfDescriptorExtractor extractor;

Mat descriptors_1, descriptors_2;

extractor.compute( img_1, keypoints_1, descriptors_1 );
extractor.compute( img_2, keypoints_2, descriptors_2 );

//-- Step 3: Matching descriptor vectors using FLANN matcher
FlannBasedMatcher matcher;
std::vector< DMatch > matches;
matcher.match( descriptors_1, descriptors_2, matches );

double max_dist = 0; double min_dist = 100;

//-- Quick calculation of max and min distances between keypoints
for( int i = 0; i < descriptors_1.rows; i++ )
{ double dist = matches[i].distance;
if( dist < min_dist ) min_dist = dist;
if( dist > max_dist ) max_dist = dist;
}

printf("-- Max dist : %f \n", max_dist );
printf("-- Min dist : %f \n", min_dist );

//-- Draw only "good" matches (i.e. whose distance is less than 2*min_dist )
//-- PS.- radiusMatch can also be used here.
std::vector< DMatch > good_matches;

for( int i = 0; i < descriptors_1.rows; i++ )
{ if( matches[i].distance < 2*min_dist )
{ good_matches.push_back( matches[i]); }
}

//-- Draw only "good" matches
Mat img_matches;
drawMatches( img_1, keypoints_1, img_2, keypoints_2,
    good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
    vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS );

//-- Show detected matches
imshow( "Good Matches", img_matches );

for( int i = 0; i < good_matches.size(); i++ )
{ printf( "-- Good Match [%d] Keypoint 1: %d  -- Keypoint 2: %d  \n", i,         good_matches[i].queryIdx, good_matches[i].trainIdx ); }

waitKey(0);

return 0;
}

/** @function readme */
void readme()
{ std::cout << " Usage: ./SURF_FlannMatcher <img1> <img2>" << std::endl; }

When I try to compile I receive an error for SurfFeatureDetector as undeclared identifier. When I right click on it and go to definition it opens it. Should I include something else? It is located in features2d.hpp which is included in cv.h file. Could you please help me with this matter?

Answer 1

Your compiler and editor are confused by the two OpenCV versions installed on your system.

First, make sure that all the settings ( include paths in Visual Studio, lib path in Visual studio linker settings and bin path -probably an environment variable) point to the same version.

Next, make sure to include all the needed headers. In OpenCV 2.4 and above, SURF and SIFT have been moved to nonfree module, so you also have to install it. Do not forget that some functions may be moved to legacy.

And if you uninstall one version of OpenCV, the editor (which doesn’t have all the parsing capabilities of the compiler) will not be confused anymore.