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OpenCV  
Open Source Computer Vision
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Point Polygon Test

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Goal

In this tutorial you will learn how to:

Theory

Code

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

#include <iostream>
using namespace cv;
using namespace std;
int main( void )
{
const int r = 100;
Mat src = Mat::zeros( Size( 4*r, 4*r ), CV_8U );
vector<Point2f> vert(6);
vert[0] = Point( 3*r/2, static_cast<int>(1.34*r) );
vert[1] = Point( 1*r, 2*r );
vert[2] = Point( 3*r/2, static_cast<int>(2.866*r) );
vert[3] = Point( 5*r/2, static_cast<int>(2.866*r) );
vert[4] = Point( 3*r, 2*r );
vert[5] = Point( 5*r/2, static_cast<int>(1.34*r) );
for( int i = 0; i < 6; i++ )
{
line( src, vert[i], vert[(i+1)%6], Scalar( 255 ), 3 );
}
vector<vector<Point> > contours;
Mat raw_dist( src.size(), CV_32F );
for( int i = 0; i < src.rows; i++ )
{
for( int j = 0; j < src.cols; j++ )
{
raw_dist.at<float>(i,j) = (float)pointPolygonTest( contours[0], Point2f((float)j, (float)i), true );
}
}
double minVal, maxVal;
Point maxDistPt; // inscribed circle center
minMaxLoc(raw_dist, &minVal, &maxVal, NULL, &maxDistPt);
minVal = abs(minVal);
maxVal = abs(maxVal);
Mat drawing = Mat::zeros( src.size(), CV_8UC3 );
for( int i = 0; i < src.rows; i++ )
{
for( int j = 0; j < src.cols; j++ )
{
if( raw_dist.at<float>(i,j) < 0 )
{
drawing.at<Vec3b>(i,j)[0] = (uchar)(255 - abs(raw_dist.at<float>(i,j)) * 255 / minVal);
}
else if( raw_dist.at<float>(i,j) > 0 )
{
drawing.at<Vec3b>(i,j)[2] = (uchar)(255 - raw_dist.at<float>(i,j) * 255 / maxVal);
}
else
{
drawing.at<Vec3b>(i,j)[0] = 255;
drawing.at<Vec3b>(i,j)[1] = 255;
drawing.at<Vec3b>(i,j)[2] = 255;
}
}
}
circle(drawing, maxDistPt, (int)maxVal, Scalar(255,255,255));
imshow( "Source", src );
imshow( "Distance and inscribed circle", drawing );
return 0;
}

Explanation

Result

Here it is:

Point_Polygon_Test_Source_Image.png
Point_Polygon_Test_Result.jpg