How Do I Calculates The Angle Of Orientation Of The Image With The Fourier Transform?

#include "opencv2/imgproc/imgproc.hpp"
#include "opencv2/highgui/highgui.hpp"
#include <stdlib.h>
#include <stdio.h>
#include <opencv2\opencv.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <stdint.h>
#include <opencv2/imgproc/imgproc.hpp>
#include <iostream>

using namespace cv;
using namespace std;


/// Global variables

Mat src, src_gray,canny_image,padded,good_f_t, threshold_image,lowerRect,imageROI,dst, detected_edges;

int edgeThresh = 1;
int lowThreshold;
int const max_lowThreshold = 100;
int ratio = 3;
int kernel_size = 3;
char* window_name = "Edge Map";

/**
 * @function CannyThreshold
 * @brief Trackbar callback - Canny thresholds input with a ratio 1:3
 */
void CannyThreshold(int, void*)
{
  /// Reduce noise with a kernel 3x3
  blur( src_gray, detected_edges, Size(3,3) );

  /// Canny detector
  Canny( detected_edges, detected_edges, lowThreshold, lowThreshold*ratio, kernel_size );

  /// Using Canny's output as a mask, we display our result
  dst = Scalar::all(0);

  src.copyTo( dst, detected_edges);
  imshow( window_name, dst );
  /*-----------------------fourier transform--------------------------*/
  Mat padded;                            //expand input image to optimal size
    int m = getOptimalDFTSize( dst.rows );
    int n = getOptimalDFTSize( dst.cols ); // on the border add zero values
    copyMakeBorder(dst, padded, 0, m - dst.rows, 0, n - dst.cols, BORDER_CONSTANT, Scalar::all(0));

    Mat planes[] = {Mat_<float>(padded), Mat::zeros(padded.size(), CV_32F)};      
    Mat complexdst;
    merge(planes, 2, complexdst);         // Add to the expanded another plane with zeros

    dft(complexdst, complexdst);            // this way the result may fit in the source matrix

    // compute the magnitude and switch to logarithmic scale
    // => log(1 + sqrt(Re(DFT(I))^2 + Im(DFT(I))^2))
    split(complexdst, planes);                   // planes[0] = Re(DFT(I), planes[1] = Im(DFT(I))
    magnitude(planes[0], planes[1], planes[0]);// planes[0] = magnitude
    Mat magdst = planes[0];

    magdst += Scalar::all(1);                    // switch to logarithmic scale
    log(magdst, magdst);

    // crop the spectrum, if it has an odd number of rows or columns
    magdst = magdst(Rect(0, 0, magdst.cols & -2, magdst.rows & -2));

    // rearrange the quadrants of Fourier image  so that the origin is at the image center
    int cx = magdst.cols/2;
    int cy = magdst.rows/2;

    Mat q0(magdst, Rect(0, 0, cx, cy));   // Top-Left - Create a ROI per quadrant
    Mat q1(magdst, Rect(cx, 0, cx, cy));  // Top-Right
    Mat q2(magdst, Rect(0, cy, cx, cy));  // Bottom-Left
    Mat q3(magdst, Rect(cx, cy, cx, cy)); // Bottom-Right

    Mat tmp;                           // swap quadrants (Top-Left with Bottom-Right)
    q0.copyTo(tmp);
    q3.copyTo(q0);
    tmp.copyTo(q3);

    q1.copyTo(tmp);                    // swap quadrant (Top-Right with Bottom-Left)
    q2.copyTo(q1);
    tmp.copyTo(q2);

    normalize(magdst, magdst, 0, 1, CV_MINMAX); // Transform the matrix with float values into a
                                            // viewable image form (float between values 0 and 1).

       imshow("spectrum magnitude", magdst);
    /*-----------------------end of fourier transform--------------------------*/

 }


/** @function main */
int main( int argc, char** argv )
{
  /// Load an image
  src = imread("C:/Users/Saha/Desktop/DSCF0563.JPG");
	resize(src, src, Size(), 0.2, 0.2, INTER_LANCZOS4);

  if( !src.data )
  { return -1; }

  /// Create a matrix of the same type and size as src (for dst)
  dst.create( src.size(), src.type() );

  /// Convert the image to grayscale
  cvtColor( src, src_gray, CV_BGR2GRAY );

  /// Create a window
  namedWindow( window_name, CV_WINDOW_AUTOSIZE );

  /// Create a Trackbar for user to enter threshold
  createTrackbar( "Min Threshold:", window_name, &lowThreshold, max_lowThreshold, CannyThreshold );

  /// Show the image
  CannyThreshold(0, 0);

  /// Wait until user exit program by pressing a key
  waitKey(0);

  return 0;
  }