Weird map orientation using sobel gradients

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I tried to follow this method of drawing orientation map http://answers.opencv.org/question/9493/fingerprint-orientation-map-through-gradient/

And i used a block size of 5x5 on my 480x320 image. The gradients i got was from 0-270 degrees. And there are constant values that keep on repeating like 44.7623 and 224.762. I wonder if my gradients are wrong.

After that, i add all the gradients in the 5x5 block and divide them by 25 (averaging) like what the link said. I divided the degrees into 8 sections of 45degree intervals and plotted them out. But it looks nothing like my original image. Can anyone tell me what's wrong? I just want to detect the core(circle-like) feature of the image.

My original image is this _________________________________________________ But my orientation map is this:

This is what I'm doing

What's wrong ? =(

I got the gradients from this method :

/// Gradient X
 cv::Sobel(original_Mat, grad_x, CV_32FC1, 1, 0, 3);

 /// Gradient Y
 cv::Sobel(original_Mat, grad_y, CV_32FC1, 0, 1, 3);

  Mat orientation = Mat(grad_x.rows, grad_y.cols, CV_32F);

 for(int i = 0; i < grad_x.rows; i++){
    for(int j = 0; j < grad_x.cols; j++){
        // Retrieve a single value
        float valueX = grad_x.at<float>(i,j);
        float valueY = 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;

    }
    }

Here's the full code.

 int main()
 {

cv::Mat original_Mat=cv::imread("Source.bmp", 1);

cv::Mat grad = cv::Mat::zeros(original_Mat.size(),CV_64F);

 /// Generate grad_x and grad_y
 cv::Mat grad_x = cv::Mat::zeros(original_Mat.size(), CV_64F); 
 cv::Mat grad_y = cv::Mat::zeros(original_Mat.size(), CV_64F);
 cv::Mat grad_angle = cv::Mat::zeros(original_Mat.size(), CV_64F);

 /// Gradient X
 cv::Sobel(original_Mat, grad_x, CV_32FC1, 1, 0, 3);

 /// Gradient Y
 cv::Sobel(original_Mat, grad_y, CV_32FC1, 0, 1, 3);

  Mat orientation = Mat(grad_x.rows, grad_y.cols, CV_32F); //to store the gradients
  Mat img=Mat(grad_x.rows, 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 < grad_x.rows; i++){
    for(int j = 0; j < grad_x.cols; j++){
        // Retrieve a single value
        float valueX = grad_x.at<float>(i,j);
        float valueY = 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;

    }
    }


int i=0,j=0;
int x1=0,x2=0;
float results;

for(int l=0;l<96;l++) //to loop all the rows
{
    int x1=(5+(l*5)); // to get 5x5 block sizes

for(int k=0;k<64;k++)//to loop all the columns
{

    int x2=(5+(k*5)); // to get 5x5 block sizes
     results=0;


           //to get the total of 5x5 gradient values
    for(i=(x1-5); i < x1; i++){
    for(j=(x2-5); j ...