How con a find a specif point through a contour?

edit

Hey, guys. I've been working on a project lately, I'm trying to create a line follower robot using the raspberry pi and it's camera module. I'm really new to opencv and I've been struggling to actually solve a problem I'm having. I'm able to track the black line that is placed over a white floor, using this tutorial. I was using it to track the center point of the line and it was working quite nicely, but I've recently found a problem with this aproach. It only works in straight lines, not in angled ones. So I have to chage it. In order to solve my issue, I tought I could track the two boundaries of the line (left side and right side), in the midle of the screen. The frame height is 480px, so I tought it'd points in the contour vector with y=240 and I tried to check this vector to find the x coordinates of said points. It works sometimes, but I can't find it consistently, as can be seen in this video. This is the code I'm using to track the line:

double trackFilteredObject(int &x, int &y, Mat threshold, Mat &cameraFeed){
    double distanceleft, distanceright, diference;

    Mat temp;
    //Rect bounding;
    double dist;
    Point teste;
    threshold.copyTo(temp);
    int contornox=0, contornoy=0, contornox2 = 0, contornoy2 = 0;

    vector< vector<Point> > contours;
    vector<Vec4i> hierarchy;
    findContours(temp, contours, hierarchy, CV_RETR_CCOMP, CV_CHAIN_APPROX_SIMPLE);
    double refArea = 0;
    bool objectFound = false;
    //drawContours(temp,contours,0,Scalar(0,255,0),1,8,hierarchy);
    if(hierarchy.size() > 0){
        int numOjbects = hierarchy.size();

        if(numOjbects <MAX_NUM_OBJECTS){
            for(int index = 0; index >=0; index = hierarchy[index][0]){
                Moments moment = moments((Mat)contours[index]);
                double area = moment.m00;
                if(area>MIN_OBJECT_AREA && area<MAX_OBJECT_AREA && area>refArea){
                    x = moment.m10/area;
                    y = moment.m01/area;
                    objectFound = true;
                    refArea = area;
                    for (int i=0; i< contours[0].size(); i++){
                                    Point coordinate_i_ofcontour = contours[0][i];
                            //usleep(2000000);
                           // cout<<coordinate_i_ofcontour<<endl;
                                if(coordinate_i_ofcontour.y == FRAME_HEIGHT/2){
                                        cout<<"I'm here"<<endl;
                                if(contornoy == 0){
                                contornoy = FRAME_HEIGHT/2;
                                            contornox = coordinate_i_ofcontour.x;
                                }else{
                                contornoy2 = FRAME_HEIGHT/2;
                                contornox2 = coordinate_i_ofcontour.x;
                                }
                                 }

                    }
                    cout<<"("<<contornox<<","<<contornoy<<endl;
                }else objectFound = false;
            }
            if(objectFound == true){

                putText(cameraFeed, "Tracking Object", Point(0,50),2,1, Scalar(0,255,0),2);
                drawLine(contornox,contornoy, cameraFeed);

                distanceleft = std::pow((pow(x-FRAME_WIDTH,2)+pow(y-(FRAME_HEIGHT/2),2)),0.5);
                distanceright = std::pow((pow(x,2)+pow(y-(FRAME_HEIGHT/2),2)),0.5);
                diference = distanceleft-distanceright;
                return(diference);
            }else if(objectFound == false){
                putText(cameraFeed, "TOO MUCH NOISE!", Point(0,50),1,2,Scalar(0,0,255),2);
                return(-10000);
            }
        }
    }

}

If any of you guys could help me to find what I'm doing wrong, I'd be very happy. Thanks in advance.