OpenCV sort points stored in Point2f vector - c++

Question

I am trying to sort the result returned by minAreaRect using the following algorithm:
Here's my code for now:
void sortPoints(Point2f* unsorted) {
Point2f sorted[4];
for (int i = 0; i < 4; i++) sorted[i] = Point(0, 0);
float middleX = (unsorted[0].x + unsorted[1].x + unsorted[2].x + unsorted[3].x) / 4;
float middleY = (unsorted[0].y + unsorted[1].y + unsorted[2].y + unsorted[3].y) / 4;
for (int i = 0; i < 4; i++) {
if (unsorted[i].x < middleX && unsorted[i].y < middleY) sorted[0] = unsorted[i];
if (unsorted[i].x > middleX && unsorted[i].y < middleY) sorted[1] = unsorted[i];
if (unsorted[i].x < middleX && unsorted[i].y > middleY) sorted[2] = unsorted[i];
if (unsorted[i].x > middleX && unsorted[i].y > middleY) sorted[3] = unsorted[i];
}
unsorted = sorted;
}
...
vector<RotatedRect> minRect( contours.size() );
for( int i = 0; i < contours.size(); i++ ) {
minRect[i] = minAreaRect( Mat(contours[i]) );
}
Point2f rect_points[4];
for( int i = 0; i < contours.size(); i++ ) {
minRect[i].points( rect_points );
sortPoints( rect_points ); /* ...they are not sorted after calling sortPoints?!? */
}
But it's not working, no compile error, but the points are not sorted. I think there's something wrong with data types.

Answer 1

The algorithm you provided only works if the 4 points belong to a rectangle parallel to x-y axis. Also the way you try to return result will not work properly. Try copying the sorted array back to unsorted. like this for ( int i=0;i<4;++i ) unsorted[i] = sorted[i];
But there is certain way you can use
#include <algorithm>
struct str{
bool operator() ( Point2f a, Point2f b ){
if ( a.y != b.y )
return a.y < b.y;
return a.x <= b.x ;
}
} comp;
int main()
{
Point2f v[4];
v[0] = Point2f(0,1);
v[1] = Point2f(-1,1);
v[2] = Point2f(2,1);
v[3] = Point2f(4,1);
sort(v,v+4,comp);
}