Vector out of range

Question

I am trying to draw a bounding box around contours using OpenCV. This is a real time application where all the images are grabbed from a camera real time, and Following is the important part of the code

RTMotionDetector.h

vector<vector<Point>> *contours;
    vector<vector<Point>> *contoursPoly;

RTMotionDetector.cpp

RTMotionDetector::RTMotionDetector(void)
{
    current = new Mat();
    currentGrey = new Mat();
    canny = new Mat();
    next = new Mat();
    absolute = new Mat();

    cam1 = new VideoCapture();
    cam2 = new VideoCapture();

    contours = new vector<vector<Point>>();
    contoursPoly = new vector<vector<Point>>();
    boundRect = new vector<Rect>();

}

double RTMotionDetector::getMSE(Mat I1, Mat I2)
{
    Mat s1;

    //Find difference
    cv::absdiff(I1, I2, s1);       // |I1 - I2|
    imshow("Difference",s1);

    //Do canny to get edges
    cv::Canny(s1,*canny,30,30,3);
    imshow("Canny",*canny);

    //Find contours
    findContours(*canny,*contours,CV_RETR_EXTERNAL,CV_CHAIN_APPROX_NONE);
    //System::Windows::Forms::MessageBox::Show(""+contours->size());

    //Draw contours
    drawContours(*current,*contours,-1,Scalar(0,0,255),2);
    for(int i=0;i<contours->size();i++)
    {
        cv::approxPolyDP(Mat((*contours)[i]),(*contoursPoly)[i],3,true);
        //boundRect[i] = boundingRect(contoursPoly[i]);
    }
}

As soon as the following part gets executed, I am getting an error

cv::approxPolyDP(Mat((*contours)[i]),(*contoursPoly)[i],3,true);

Here is the error I am getting.

If I comment out that piece of code, then no issues. I know this is ArrayIndexOutOfBounds issue but I really can't find a fix. May be because I am new to Windows Programming.

It is very important that contours stay as a pointer instead of local variable, because local variable slowed the program in an unbelievable way.

Answer 1

You need to find which access to which vector has gone beyond its bounds.

You loop til the size of contours,

for(int i=0;i<contours->size();i++)

but then access (*contoursPoly)[i]

I would hazard a guess that the contoursPoly has gone beyond its bounds, which you can check by breaking into the debugger as suggested.

Changing the loop to

for(int i=0;i<contours->size() && i<contoursPoly->size();i++)

might solve the immediate problem.