Point Polygon Test — OpenCV 2.4.13.4 documentation

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# Point Polygon Test

## Goal

In this tutorial you will learn how to:

- Use the OpenCV function pointPolygonTest

## Theory

## Code

This tutorial code’s is shown lines below. You can also download it from here

    #include "opencv2/highgui/highgui.hpp"
    #include "opencv2/imgproc/imgproc.hpp"
    #include <iostream>
    #include <stdio.h>
    #include <stdlib.h>

    using namespace cv;
    using namespace std;

    /** @function main */
    int main( int argc, char** argv )
    {
      /// Create an image
      const int r = 100;
      Mat src = Mat::zeros( Size( 4*r, 4*r ), CV_8UC1 );

      /// Create a sequence of points to make a contour:
      vector<Point2f> vert(6);

      vert[0] = Point( 1.5*r, 1.34*r );
      vert[1] = Point( 1*r, 2*r );
      vert[2] = Point( 1.5*r, 2.866*r );
      vert[3] = Point( 2.5*r, 2.866*r );
      vert[4] = Point( 3*r, 2*r );
      vert[5] = Point( 2.5*r, 1.34*r );

      /// Draw it in src
      for( int j = 0; j < 6; j++ )
         { line( src, vert[j],  vert[(j+1)%6], Scalar( 255 ), 3, 8 ); }

      /// Get the contours
      vector<vector<Point> > contours; vector<Vec4i> hierarchy;
      Mat src_copy = src.clone();

      findContours( src_copy, contours, hierarchy, RETR_TREE, CHAIN_APPROX_SIMPLE);

      /// Calculate the distances to the contour
      Mat raw_dist( src.size(), CV_32FC1 );

      for( int j = 0; j < src.rows; j++ )
         { for( int i = 0; i < src.cols; i++ )
              { raw_dist.at<float>(j,i) = pointPolygonTest( contours[0], Point2f(i,j), true ); }
         }

      double minVal; double maxVal;
      minMaxLoc( raw_dist, &minVal, &maxVal, 0, 0, Mat() );
      minVal = abs(minVal); maxVal = abs(maxVal);

      /// Depicting the  distances graphically
      Mat drawing = Mat::zeros( src.size(), CV_8UC3 );

      for( int j = 0; j < src.rows; j++ )
         { for( int i = 0; i < src.cols; i++ )
              {
                if( raw_dist.at<float>(j,i) < 0 )
                  { drawing.at<Vec3b>(j,i)[0] = 255 - (int) abs(raw_dist.at<float>(j,i))*255/minVal; }
                else if( raw_dist.at<float>(j,i) > 0 )
                  { drawing.at<Vec3b>(j,i)[2] = 255 - (int) raw_dist.at<float>(j,i)*255/maxVal; }
                else
                  { drawing.at<Vec3b>(j,i)[0] = 255; drawing.at<Vec3b>(j,i)[1] = 255; drawing.at<Vec3b>(j,i)[2] = 255; }
              }
         }

      /// Create Window and show your results
      char* source_window = "Source";
      namedWindow( source_window, CV_WINDOW_AUTOSIZE );
      imshow( source_window, src );
      namedWindow( "Distance", CV_WINDOW_AUTOSIZE );
      imshow( "Distance", drawing );

      waitKey(0);
      return(0);
    }

## Explanation

## Result

1. Here it is:

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