Need Help in Marker detection using openCV and ARToolKit

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Hello Everyone,

I am currently working on a project which requires marker detection and then over laying it with some other image. I am not able to understand how marker detection works and how can I program it with OpenCV. The ARToolkit examples are in OpenGL but I need my program to be in OpenCV.

The problem is I am not able to under stand how do I detect the marker and get its co- ordinates.

I have attached my code Please guide me on what should I do next I just need to learn to detect a marker any marker would do.

int pattID  = 0;
char           *patt_name      = "Data/patt.hiro";
double          patt_width     = 80.0;
double          patt_center[2] = {0.0, 0.0};
double          patt_trans[3][4];

int main()
{
    CvCapture* capture = cvCaptureFromCAM(0);
    if(!capture)
    {
        printf("No Cam Connected");
        getch();
        return -1;
    }
IplImage* frame = cvQueryFrame(capture);

//Load (default) camera parameters
ARParam cameraParam;
if(arParamLoad("camera_para.dat",1,&cameraParam) < 0)
{
    printf("Camera calibration parameters file Load Error\n");
    getch();
    return -1;
}

//Initalize Camera Parameters
arInitCparam(&cameraParam);

//Load Hiro Pattern
if((pattID = arLoadPatt(patt_name)) < 0)
{
    printf("Pattern File Load Error");
    getch();
    return -1;
}

while(1)
{
    ARMarkerInfo* markerInfo = NULL;
    int markerNum = -1;

    IplImage* img = cvQueryFrame(capture);


    //Code for Resizing of image
/* input new width and height.

arParamChangeSize(&cameraParam, frame.rows, frame.cols, &cameraParam);

*/

// Marker Detection
    if (arDetectMarker((ARUint8 *)frame->imageData, 150, &markerInfo, &markerNum) < 0) 
 {
    printf("Marker Detector Error");
    getch();
    return -1;
 }

 //Check which one of the found markers is the one we seek
int k = -1;
    for (int i = 0; i < markerNum; i++) 
    {
        if (pattID == markerInfo[i].id) 
        {
            if (k == -1) 
            {
                k = i;
            } 
            else if (markerInfo[k].cf < markerInfo[i].cf) 
            {
                k = i;
            }
        }
    }

//Please Let me know how to proceed further in this code. }