Detetcting intersection between 2 line in webcam feed opencv - opencv

Question

i'm trying to detect the intersection between two line in webcam feed. Here's the screenshot of what i already have
I try to find the intersection between my red and green line.
And here's the code of what i already have
#include "stdafx.h"
#include <cv.h>
#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <highgui.h>
IplImage* imgTracking;
int lastX = -1;
int lastY = -1;
//This function threshold the HSV image and create a binary image
IplImage* GetThresholdedImage(IplImage* imgHSV){
IplImage* imgThresh=cvCreateImage(cvGetSize(imgHSV),IPL_DEPTH_8U, 1);
cvInRangeS(imgHSV, cvScalar(170,160,60), cvScalar(180,2556,256), imgThresh);
return imgThresh;
}
void trackObject(IplImage* imgThresh){
// Calculate the moments of 'imgThresh'
CvMoments *moments = (CvMoments*)malloc(sizeof(CvMoments));
cvMoments(imgThresh, moments, 1);
double moment10 = cvGetSpatialMoment(moments, 1, 0);
double moment01 = cvGetSpatialMoment(moments, 0, 1);
double area = cvGetCentralMoment(moments, 0, 0);
// if the area<1000, I consider that the there are no object in the image and it's because of the noise, the area is not zero
if(area>1000){
// calculate the position of the ball
int posX = moment10/area;
int posY = moment01/area;
if(lastX>=0 && lastY>=0 && posX>=0 && posY>=0)
{
// Draw a yellow line from the previous point to the current point
cvLine(imgTracking, cvPoint(posX, posY), cvPoint(lastX, lastY), cvScalar(0,0,255), 4);
}
lastX = posX;
lastY = posY;
}
cvLine(imgTracking,cv::Point(100,300) , cv::Point(600,300),cv::Scalar(0,200,0),2,8);
free(moments);
}
bool intersection(cv::Point lastX, cv::Point lastY, cv::Point , cv::Point())
{
}
/*
void imaginaryline()
{
cv::Mat img = cv::Mat::zeros(500, 500, CV_8UC3);
cv::line(img, cv::Point(100,200) , cv::Point(400,100),cv::Scalar(0,200,0),2,8);
}*/
int main(){
CvCapture* capture =0;
capture = cvCaptureFromCAM(0);
if(!capture){
printf("Capture failure\n");
return -1;
}
IplImage* frame=0;
frame = cvQueryFrame(capture);
if(!frame) return -1;
//create a blank image and assigned to 'imgTracking' which has the same size of original video
imgTracking=cvCreateImage(cvGetSize(frame),IPL_DEPTH_8U, 3);
cvZero(imgTracking); //covert the image, 'imgTracking' to black
cvNamedWindow("Video");
cvNamedWindow("Ball");
//iterate through each frames of the video
while(true){
frame = cvQueryFrame(capture);
if(!frame) break;
frame=cvCloneImage(frame);
cvSmooth(frame, frame, CV_GAUSSIAN,3,3); //smooth the original image using Gaussian kernel
IplImage* imgHSV = cvCreateImage(cvGetSize(frame), IPL_DEPTH_8U, 3);
cvCvtColor(frame, imgHSV, CV_BGR2HSV); //Change the color format from BGR to HSV
IplImage* imgThresh = GetThresholdedImage(imgHSV);
cvSmooth(imgThresh, imgThresh, CV_GAUSSIAN,3,3); //smooth the binary image using Gaussian kernel
//track the possition of the ball
trackObject(imgThresh);
printf("Pos X = %d", lastX);
printf("Pos Y = %d", lastY);
// Add the tracking image and the frame
cvAdd(frame, imgTracking, frame);
cvShowImage("Ball", imgThresh);
cvShowImage("Video", frame);
//Clean up used images
cvReleaseImage(&imgHSV);
cvReleaseImage(&imgThresh);
cvReleaseImage(&frame);
//Wait 10mS
int c = cvWaitKey(10);
//If 'ESC' is pressed, break the loop
if((char)c==27 ) break;
}
cvDestroyAllWindows() ;
cvReleaseImage(&imgTracking);
cvReleaseCapture(&capture);
return 0;
}
Thank you for your attention guys, i waited for any of your response
UPDATE :
Thanks to Sebastian Schmitz, i sollved it. Here's my code
void checkIntersection(int line, int lastY, int y)
{
if(lastY << line && y >= line || lastY > line && y <= line)
{
printf("intersection detected");
}
}
void trackObject(IplImage* imgThresh){
// Calculate the moments of 'imgThresh'
CvMoments *moments = (CvMoments*)malloc(sizeof(CvMoments));
cvMoments(imgThresh, moments, 1);
double moment10 = cvGetSpatialMoment(moments, 1, 0);
double moment01 = cvGetSpatialMoment(moments, 0, 1);
double area = cvGetCentralMoment(moments, 0, 0);
// if the area<1000, I consider that the there are no object in the image and it's because of the noise, the area is not zero
if(area>1000){
// calculate the position of the ball
int posX = moment10/area;
int posY = moment01/area;
if(lastX>=0 && lastY>=0 && posX>=0 && posY>=0)
{
// Draw a yellow line from the previous point to the current point
cvLine(imgTracking, cvPoint(posX, posY), cvPoint(lastX, lastY), cvScalar(0,0,255), 4);
}
checkIntersection(300, lastY, posY);
lastX = posX;
lastY = posY;
}
cvLine(imgTracking,cv::Point(100,300) , cv::Point(600,300),cv::Scalar(0,200,0),2,8);
cvRectangle(imgTracking,cv::Point(400,400), cv::Point(450,450),cv::Scalar(0,200,0),2,8);
free(moments);
}
i put the call for checkintersection function inside trackobject function so i dont have to change variable posY into global which lead to many error.
Thank you all for your response

Answer 1

If the line is always perfectly horiontal, it will be enough to test if the y coordinate of your last point is on one side of the line and your current Point on the other:
//Pseudocode:
int line = 20; //horizontal line on y-coordinate "20"
while(tracking == true){
int lastY = posY;
int y = getCoordinate().getY(); //call the y-coordinate of your current point
checkIntersection(line, lastY, y)
}
checkIntersection(int line, int lastY, int y){
if(lastY < line && y >= line ||
lastY > line && y <= line ){
print("intersection detected")
//optional additional check if point is between endpoint of line if you have to
}
}