I Have prob with this coding related to find the contours - c++

Question

I want to find the centroid of each contour.for that i take some sample code and test it..i have a prob with this coding.i got an error...Please help me to resolve that...this very useful for me...Thanks in advance...I use windows platform with visual studio 2008
#include <cv.h>
#include <highgui.h>
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
Mat src;
Mat src_gray;
int thresh = 100;
int max_thresh = 255;
RNG rng(12345);
/// Function header
void thresh_callback(int, void* );
/** #function main */
int main( int argc, char** argv )
{
/// Load source image and convert it to gray
IplImage* src = cvLoadImage( "TEST2.jpg");
/// Convert image to gray and blur it
cvtColor( src, src_gray, CV_BGR2GRAY );
blur( src_gray, src_gray, Size(3,3) );
/// Create Window
char* source_window = "Source";
namedWindow( source_window, CV_WINDOW_AUTOSIZE );
imshow( source_window, src );
createTrackbar( "Canny thresh:","Source", &thresh, max_thresh, thresh_callback );
thresh_callback(0,0);
waitKey(0);
return(0);
}
/** #function thresh_callback */
void thresh_callback(int, void* )
{
Mat canny_output;
vector<vector<Point>> contours;
vector<Vec4i> hierarchy;
/// Detect edges using canny
Canny( src_gray, canny_output, thresh,thresh*2,3);
/// Find contours
findContours( canny_output, contours, hierarchy, CV_RETR_TREE, CV_CHAIN_APPROX_SIMPLE, Point(0, 0) );
/// Get the moments
vector<Moments> mu(contours.size());
for( int i = 0; i < contours.size(); i++ )
{
mu[i] = moments( contours[i], false );
}
/// Get the mass centers:
vector<Point2f> mc( contours.size() );
for( int i = 0; i < contours.size(); i++ )
{
mc[i] = Point2f( mu[i].m10/mu[i].m00 , mu[i].m01/mu[i].m00 );
}
/// Draw contours
Mat drawing = Mat::zeros( canny_output.size(), CV_8UC3 );
for( int i = 0; i< contours.size(); i++ )
{
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
circle( drawing, mc[i], 4, color, -1, 8, 0 );
}
/// Show in a window
namedWindow( "Contours", CV_WINDOW_AUTOSIZE );
imshow( "Contours", drawing );
/// Calculate the area with the moments 00 and compare with the result of the OpenCV function
printf("\t Info: Area and Contour Length \n");
for( int i = 0; i< contours.size(); i++ )
{
printf(" * Contour[%d] - Area (M_00) = %.2f - Area OpenCV: %.2f - Length: %.2f \n", i, mu[i].m00, contourArea(contours[i]), arcLength( contours[i], true ) );
Scalar color = Scalar( rng.uniform(0, 255), rng.uniform(0,255), rng.uniform(0,255) );
drawContours( drawing, contours, i, color, 2, 8, hierarchy, 0, Point() );
circle( drawing, mc[i], 4, color, -1, 8, 0 );
}
}
The error lik...
Error 2 error C2664: 'cv::moments' : cannot convert parameter 1 from 'std::vector<_Ty>' to 'const cv::Mat &' d:\aranga_try\new_opencv\new_opencv\auto_focustest.cpp 57 New_opencv
Error 8 error C2664: 'cv::contourArea' : cannot convert parameter 1 from 'std::vector<_Ty>' to 'const cv::Mat &' d:\aranga_try\new_opencv\new_opencv\auto_focustest.cpp 84 New_opencv
Error 9 error C2664: 'cv::arcLength' : cannot convert parameter 1 from 'std::vector<_Ty>' to 'const cv::Mat &' d:\aranga_try\new_opencv\new_opencv\auto_focustest.cpp 84 New_opencv

Answer 1

You need to explicitly convert std::vector<cv::Point> to cv::Mat by calling
template<typename _Tp> explicit Mat(const vector<_Tp>& vec, bool copyData=false);
After getting the matrix, you can compute moments, area or perimeter. For example, to compute area:
double area = cv::contourArea(cv::Mat(contours[i], false));