Rotation Detection based on Template Matching

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I have a source image and several template images. These template images are rotated by different degrees. If the template image is not rotated (or rotated by 0 degree), I can use the attached code to find the matched pattern in the source image. However, if the template image is rotated, the template matching method in OpenCV might not work. How can I revise the code to enable it to detect the matched rotated pattern, as well as the angle that it is rotated by?

Thanks in advance.

Source image: C:\fakepath\O.jpg Template image: C:\fakepath\T.jpg Template image rotated by 30 degrees: C:\fakepath\Tr30.jpg

cpp file: #include "opencv2/highgui/highgui.hpp" #include "opencv2/imgproc/imgproc.hpp" #include <iostream> #include <stdio.h> #include <math.h>

using namespace std;
using namespace cv;

/// Global Variables
Mat img; Mat templ; Mat result;

char* result_window = "Result window";

int main( int argc, char** argv )
{
  /// Load image and template
  img = imread( argv[1], 1 );
  templ = imread( argv[2], 1 );

  /// Create windows
  namedWindow( result_window, CV_WINDOW_AUTOSIZE );

  int result_cols =  img.cols - templ.cols + 1;
  int result_rows = img.rows - templ.rows + 1;

  result.create( result_cols, result_rows, CV_32FC1 );

  /// Do the Matching and Normalize
  matchTemplate( img, templ, result, CV_TM_SQDIFF_NORMED );
  normalize( result, result, 0, 1, NORM_MINMAX, -1, Mat() );


  double minVal; double maxVal; Point minLoc; Point maxLoc;
  minMaxLoc( result, &minVal, &maxVal, &minLoc, &maxLoc, Mat() );


  /// Show me what you got
  rectangle( result, minLoc, Point( minLoc.x + templ.cols , minLoc.y + templ.rows ), Scalar::all(0), 2, 8, 0 );


  imshow( result_window, result );

  waitKey(0);
  return 0;
}