OpenCV  4.10.0-dev
Open Source Computer Vision
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Examples of how intersectConvexConvex works

* Author: Steve Nicholson
* A program that illustrates intersectConvexConvex in various scenarios
using namespace cv;
using namespace std;
// Create a vector of points describing a rectangle with the given corners
static vector<Point> makeRectangle(Point topLeft, Point bottomRight)
vector<Point> rectangle;
rectangle.push_back(Point(bottomRight.x, topLeft.y));
rectangle.push_back(Point(topLeft.x, bottomRight.y));
return rectangle;
static vector<Point> makeTriangle(Point point1, Point point2, Point point3)
vector<Point> triangle;
return triangle;
// Run intersectConvexConvex on two polygons then draw the polygons and their intersection (if there is one)
// Return the area of the intersection
static float drawIntersection(Mat &image, vector<Point> polygon1, vector<Point> polygon2, bool handleNested = true)
vector<Point> intersectionPolygon;
vector<vector<Point> > polygons;
float intersectArea = intersectConvexConvex(polygon1, polygon2, intersectionPolygon, handleNested);
if (intersectArea > 0)
Scalar fillColor(200, 200, 200);
// If the input is invalid, draw the intersection in red
if (!isContourConvex(polygon1) || !isContourConvex(polygon2))
fillColor = Scalar(0, 0, 255);
fillPoly(image, intersectionPolygon, fillColor);
polylines(image, polygons, true, Scalar(0, 0, 0));
return intersectArea;
static void drawDescription(Mat &image, int intersectionArea, string description, Point origin)
const size_t bufSize=1024;
char caption[bufSize];
snprintf(caption, bufSize, "Intersection area: %d%s", intersectionArea, description.c_str());
putText(image, caption, origin, FONT_HERSHEY_SIMPLEX, 0.6, Scalar(0, 0, 0));
static void intersectConvexExample()
Mat image(610, 550, CV_8UC3, Scalar(255, 255, 255));
float intersectionArea;
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 10), Point(50, 50)),
makeRectangle(Point(20, 20), Point(60, 60)));
drawDescription(image, (int)intersectionArea, "", Point(70, 40));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 70), Point(35, 95)),
makeRectangle(Point(35, 95), Point(60, 120)));
drawDescription(image, (int)intersectionArea, "", Point(70, 100));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 130), Point(60, 180)),
makeRectangle(Point(20, 140), Point(50, 170)),
drawDescription(image, (int)intersectionArea, " (handleNested true)", Point(70, 160));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 190), Point(60, 240)),
makeRectangle(Point(20, 200), Point(50, 230)),
drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 220));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 250), Point(60, 300)),
makeRectangle(Point(20, 250), Point(50, 290)),
drawDescription(image, (int)intersectionArea, " (handleNested true)", Point(70, 280));
// These rectangles share an edge so handleNested can be false and an intersection is still found
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 310), Point(60, 360)),
makeRectangle(Point(20, 310), Point(50, 350)),
drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 340));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 370), Point(60, 420)),
makeRectangle(Point(20, 371), Point(50, 410)),
drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 400));
// A vertex of the triangle lies on an edge of the rectangle so handleNested can be false and an intersection is still found
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 430), Point(60, 480)),
makeTriangle(Point(35, 430), Point(20, 470), Point(50, 470)),
drawDescription(image, (int)intersectionArea, " (handleNested false)", Point(70, 460));
// Show intersection of overlapping rectangle and triangle
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 490), Point(40, 540)),
makeTriangle(Point(25, 500), Point(25, 530), Point(60, 515)),
drawDescription(image, (int)intersectionArea, "", Point(70, 520));
// This concave polygon is invalid input to intersectConvexConvex so it returns an invalid intersection
vector<Point> notConvex;
notConvex.push_back(Point(25, 560));
notConvex.push_back(Point(25, 590));
notConvex.push_back(Point(45, 580));
notConvex.push_back(Point(60, 600));
notConvex.push_back(Point(60, 550));
notConvex.push_back(Point(45, 570));
intersectionArea = drawIntersection(image,
makeRectangle(Point(10, 550), Point(50, 600)),
drawDescription(image, (int)intersectionArea, " (invalid input: not convex)", Point(70, 580));
imshow("Intersections", image);
int main()
n-dimensional dense array class
Definition mat.hpp:812
_Tp y
y coordinate of the point
Definition types.hpp:202
_Tp x
x coordinate of the point
Definition types.hpp:201
#define CV_8UC3
Definition interface.h:90
void imshow(const String &winname, InputArray mat)
Displays an image in the specified window.
int waitKey(int delay=0)
Waits for a pressed key.
void fillPoly(InputOutputArray img, InputArrayOfArrays pts, const Scalar &color, int lineType=LINE_8, int shift=0, Point offset=Point())
Fills the area bounded by one or more polygons.
void putText(InputOutputArray img, const String &text, Point org, int fontFace, double fontScale, Scalar color, int thickness=1, int lineType=LINE_8, bool bottomLeftOrigin=false)
Draws a text string.
void polylines(InputOutputArray img, InputArrayOfArrays pts, bool isClosed, const Scalar &color, int thickness=1, int lineType=LINE_8, int shift=0)
Draws several polygonal curves.
float intersectConvexConvex(InputArray p1, InputArray p2, OutputArray p12, bool handleNested=true)
Finds intersection of two convex polygons.
bool isContourConvex(InputArray contour)
Tests a contour convexity.
int main(int argc, char *argv[])
Definition highgui_qt.cpp:3
"black box" representation of the file storage associated with a file on disk.
Definition core.hpp:102
STL namespace.