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Object localization program crashing at approxPolyDP function[SOLVED]

asked 2020-02-10 01:01:09 -0500

Shapy gravatar image

updated 2020-02-11 20:21:08 -0500

supra56 gravatar image

Hello There! I am trying to find the location of a green ball in the frame of a video stream. I am using a logitech webcam for the program. I am first thresholding the green ball out of the video frame and performing countour finding. Then I am trying to perform enclosing circles function but my program crashes before at the approxPolyDP() function. I am programming in C++, with Opencv 4.1.0.

#include <QCoreApplication>
#include <opencv2/core.hpp>
#include <opencv2/opencv.hpp>
#include <opencv2/imgcodecs.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/video.hpp>
#include <iostream>
#include <string>
#include <vector>

using namespace std;
using namespace cv;

//Declaring variables globally
Mat frame,frame_copy,frame_down,frame_blur,frame_hsv, frame_gray, frame_threshold, frame_erode,  frame_dilate, frame_canny ;
const int max_value_H = 360/2;
const int max_value = 255;
int low_H = 29, low_S = 86, low_V = 6;
int high_H = 64, high_S = max_value, high_V = max_value;
RNG rng(12345);

int main(int argc, char *argv[])
QCoreApplication a(argc, argv);

VideoCapture stream = VideoCapture(1);         //Opening video streaming from external camera
if(!stream.isOpened()){cout<<"VideoStream not available!"<<endl; return 0;}

    frame_copy = frame;     


    blur(frame_down, frame_blur, Size(3,3));

    inRange(frame_hsv, Scalar(low_H, low_S, low_V), Scalar(high_H, high_S, high_V), frame_threshold);   
    Mat element = getStructuringElement( MORPH_OPEN,Size(5, 5) );                         

    erode( frame_threshold, frame_erode, element );      
    dilate( frame_erode, frame_dilate, element );   


    vector<vector<Point> > contours;
    vector<Vec4i> hierarchy;
    vector<vector<Point>>  contours_poly( contours.size() );
    vector<Rect> boundRect( contours.size() );
    vector<Point2f>centers( contours.size() );
    vector<float>radius( contours.size() );

    findContours( frame_canny, contours, RETR_TREE, CHAIN_APPROX_SIMPLE );

    Mat drawing = Mat::zeros( frame_canny.size(), CV_8UC3 );

        for( size_t i = 0; i< contours.size(); i++ )
//            boundRect[i] = boundingRect( contours_poly[i] );
            minEnclosingCircle( contours_poly[i], centers[i], radius[i] );
        for( size_t i = 0; i< contours.size(); i++ )                                             //Drawing contours that were found
            Scalar color = Scalar( rng.uniform(0, 256), rng.uniform(0,256), rng.uniform(0,256) );
//            drawContours( drawing, contours_poly, (int)i, color );
//            rectangle( drawing, boundRect[i].tl(), boundRect[i].br(), color, 2 );
            circle( drawing, centers[i], (int)radius[i], color, 2 );



return a.exec();

Please can anyone guide me as to what I am doing wrong and/or suggest anything better?


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what is error message?

LBerger gravatar imageLBerger ( 2020-02-10 02:31:51 -0500 )edit

It doesn't give an error message. It simply crashes without a message when a green circular object comes in front of the camera.

Shapy gravatar imageShapy ( 2020-02-10 03:17:20 -0500 )edit

1 answer

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answered 2020-02-10 23:51:39 -0500

updated 2020-02-11 03:27:02 -0500

You are declaring other vector variables i.e. contours_poly, boundRect, centers, radius before using findContours() function. The issue with this is that, the vector "contours" is still empty when you're calling "contours.size()", while declaring this vector variables. They should be declared after calling "findContours()" as follows:

vector<vector<Point> > contours;
vector<Vec4i> hierarchy;

findContours( frame_canny, contours, RETR_TREE, CHAIN_APPROX_SIMPLE );

vector<vector<Point>>  contours_poly( contours.size() );
vector<Rect> boundRect( contours.size() );
vector<Point2f>centers( contours.size() );
vector<float>radius( contours.size() );

I tested the revised code and it is working. I hope this helps.

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Thanks! That helped!

Shapy gravatar imageShapy ( 2020-02-11 06:09:52 -0500 )edit
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Asked: 2020-02-10 01:01:09 -0500

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Last updated: Feb 11