# Extract the coordinates of a point OpenCV C + + [closed]

Hello,

I want to extract a specific point in vector

```
vector <vector <Point>> contours_poly (contours.size ());
```

but I could not extract its coordinates (X and Y) because I used matrices. Here is my code:

```
vector<vector<Point> > contours;
vector<vector<Point> > contours_poly( contours.size() );
for(size_t i = 0; i < contours.size(); i++ )
{
approxPolyDP( Mat(contours[i]), contours_poly[i], 2, true );
}
```

Merci.

what goes wrong ?

I can't extract the coordinates of a specific point(the X and the Y) of my vector "contours_poly"

X = contours_poly[ contour_id ][ point_id ] .x;

(note, that the contours_poly vectors will have less points than the original contour due to the approx.)

Thanks a lot :D