Linking error of openCV 2.3.1 findContours function

Question

when i am trying to run the finding squares code with Visual Studio 2008 , it gives the following error.

1>ANPR.obj : error LNK2001: unresolved external symbol "public: virtual class cv::GlBuffer __thiscall cv::_InputArray::getGlBuffer(void)const " (?getGlBuffer@_InputArray@cv@@UBE?AVGlBuffer@2@XZ)
1>ANPR.obj : error LNK2001: unresolved external symbol "public: virtual class cv::GlTexture __thiscall cv::_InputArray::getGlTexture(void)const " (?getGlTexture@_InputArray@cv@@UBE?AVGlTexture@2@XZ)
1>ANPR.obj : error LNK2001: unresolved external symbol "public: virtual class  cv::gpu::GpuMat __thiscall cv::_InputArray::getGpuMat(void)const " (?getGpuMat@_InputArray@cv@@UBE?AVGpuMat@gpu@2@XZ)

Code :

#include <cv.h>
#include <highgui.h>

using namespace cv;

double angle( cv::Point pt1, cv::Point pt2, cv::Point pt0 ) 
{
    double dx1 = pt1.x - pt0.x;
    double dy1 = pt1.y - pt0.y;
    double dx2 = pt2.x - pt0.x;
    double dy2 = pt2.y - pt0.y;
    return (dx1*dx2 + dy1*dy2)/sqrt((dx1*dx1 + dy1*dy1)*(dx2*dx2 + dy2*dy2) + 1e-10);
}


void find_squares(Mat& image, vector<vector<Point> >& squares)
{
    // blur will enhance edge detection
    Mat blurred(image);
    medianBlur(image, blurred, 9);

    Mat gray0(blurred.size(), CV_8U), gray;
    vector<vector<Point> > contours;

    // find squares in every color plane of the image
    for (int c = 0; c < 3; c++)
    {
        int ch[] = {c, 0};
        mixChannels(&blurred, 1, &gray0, 1, ch, 1);

        // try several threshold levels
        const int threshold_level = 2;
        for (int l = 0; l < threshold_level; l++)
        {
            // Use Canny instead of zero threshold level!
            // Canny helps to catch squares with gradient shading
            if (l == 0)
            {
                Canny(gray0, gray, 10, 20, 3); // 

                // Dilate helps to remove potential holes between edge segments
                dilate(gray, gray, Mat(), Point(-1,-1));
            }
            else
            {
                    gray = gray0 >= (l+1) * 255 / threshold_level;
            }

            // Find contours and store them in a list
            findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

            // Test contours
            vector<Point> approx;
            for (size_t i = 0; i < contours.size(); i++)
            {
                // approximate contour with accuracy proportional
                // to the contour perimeter
                approxPolyDP(Mat(contours[i]), approx, arcLength(Mat(contours[i]), true)*0.02, true);

                // Note: absolute value of an area is used because
                // area may be positive or negative - in accordance with the
                // contour orientation
                if (approx.size() == 4 &&
                        fabs(contourArea(Mat(approx))) > 1000 &&
                        isContourConvex(Mat(approx)))
                {
                        double maxCosine = 0;

                        for (int j = 2; j < 5; j++)
                        {
                                double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
                                maxCosine = MAX(maxCosine, cosine);
                        }

                        if (maxCosine < 0.3)
                                squares.push_back(approx);
                }
           }
       }
     }
   }
int main()
{    
    Mat img = imread("peppers.jpg");
    cvtColor(img, img, CV_RGB2GRAY);
    vector<vector<Point> > squares;
    find_squares(img, squares);

    std::cout << "squares size: " << squares.size() << std::endl;
    getchar();

    return 0;
 }

Can somebody help me to solve this? I tried openCV 2.4.2.It gave the same linking error. thankz

Answer 1

These errors are related to the linking process, and the symbols you mentioned belong to the opencv_core library.

Make sure you've added this library as a dependency of your project. Go to Configuration Properties > Linker > Input and add: opencv_core242.lib

For more instructions on how to configure Visual Studio & OpenCV, check this thread .