Question

What am I doing wrong here?

vector <vector<Point> > contourElement;

for (int counter = 0; counter < contours -> size (); counter ++)
{   
    contourElement.push_back (contours -> at (counter));

    const Point *elementPoints [1] = {contourElement.at (0)};
    int numberOfPoints [] = {contourElement.at (0).size ()};

    fillPoly (contourMask, elementPoints, numberOfPoints, 1, Scalar (0, 0, 0), 8);

I keep getting an error on the const Point part. The compiler says

error: cannot convert 'std::vector<cv::Point_<int>, std::allocator<cv::Point_<int> > >' to 'const cv::Point*' in initialization

What am I doing wrong? (PS: Obviously ignore the missing bracket at the end of the for loop due to this being only part of my code)

Answer 1

Let’s analyse the offending line:

const Point *elementPoints [1] = { contourElement.at(0) };

You declared contourElement as vector <vector<Point> >, which means that contourElement.at(0) returns a vector<Point> and not a const cv::Point*. So that’s the first error.

In the end, you need to do something like:

vector<Point> tmp = contourElement.at(0);
const Point* elementPoints[1] = { &tmp[0] };
int numberOfPoints = (int)tmp.size();

Later, call it as:

fillPoly (contourMask, elementPoints, &numberOfPoints, 1, Scalar (0, 0, 0), 8);