Calculates the angle of orientation of the image with the gradient method

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Hello, I have an image I applied the gradient method for the orientation angle of the latter. following the execution of this code I images for gradient directions Dx and DY. So I need to find the orientation angle. Personally I do not know where is the problem because I have no error! Please help me

  #include <iostream>
    #include <stdio.h>
    #include <stdlib.h>

    #include "opencv2/highgui/highgui.hpp"
    #include "opencv2/imgproc/imgproc.hpp"
    #include "opencv2/core/core.hpp"

    using namespace std;
    using namespace cv;
    //#include "Functions.h"
    int main()
    {
    Mat image;
    //image = imread("lena.jpg",1);
    image = imread("uEyeImg0.tif",1);
    if(image.empty())
    {
    cout << "Could not open or find the image" << std::endl ;
    return -1;
    }

    /// Convert it to gray
    //cvtColor( image, image, CV_RGB2GRAY );
    //resize(image,image,Size(0,0),0.5,0.5,INTER_LINEAR);
    namedWindow("Image", CV_WINDOW_AUTOSIZE );
    imshow("Image", image);
    /// Generate grad_x and grad_y
    Mat grad_x, grad_y;
    Mat abs_grad_x, abs_grad_y;
    int scale = 1;
    int delta = 0;
    int ddepth = CV_16S;
    Mat grad;


    /// Gradient X
    //Scharr( image, grad_x, ddepth, 1, 0, scale, delta, BORDER_DEFAULT );
    Sobel( image, grad_x, ddepth, 1, 0, 3, scale, delta, BORDER_DEFAULT );
    convertScaleAbs( grad_x, abs_grad_x );

    /// Gradient Y
    // Scharr( image, grad_y, ddepth, 0, 1, scale, delta, BORDER_DEFAULT );
    Sobel( image, grad_y, ddepth, 0, 1, 3, scale, delta, BORDER_DEFAULT );
    convertScaleAbs( grad_y, abs_grad_y );
    /// Total Gradient (approximate)

    addWeighted( abs_grad_x, 0.5, abs_grad_y, 0.5, 0, grad );




     Mat orientation = Mat(abs_grad_x.rows, abs_grad_y.cols, CV_32F); //to store the gradients
      Mat img=Mat(abs_grad_x.rows, abs_grad_y.cols, CV_32F);//to draw out the map
      img = cv::Scalar(255,255,255);//all white


     // Calculate orientations of gradients --> in degrees
    // Loop over all matrix values and calculate the accompanied orientation

     for(int i = 0; i < abs_grad_x.rows; i++){
        for(int j = 0; j < abs_grad_x.cols; j++){
            // Retrieve a single value

            float valueX = abs_grad_x.at<float>(i,j);
            float valueY = abs_grad_x.at<float>(i,j);
            // Calculate the corresponding single direction, done by applying the arctangens function
            float result = fastAtan2(valueX,valueY);
            // Store in orientation matrix element
            orientation.at<float>(i,j) = result;

        }
     }

    namedWindow("ImageSobel", CV_WINDOW_AUTOSIZE );
    imshow( "ImageSobel", grad );

    namedWindow("ImageSobelGx", CV_WINDOW_AUTOSIZE );
    imshow( "ImageSobelGx", abs_grad_x );

    namedWindow("ImageSobelGy", CV_WINDOW_AUTOSIZE );
    imshow( "ImageSobelGy", abs_grad_y );

    waitKey(0);
    return 0;
    }