Extracting two hog feature and comparing by vectors of descriptor in opencv (example source code)

I am wondering that two hog features can compare or not.

There was a article about this question on this page ->
http://stackoverflow.com/questions/11626140/extracting-hog-features-using-opencv

This article introduces that to compare the descriptor values of HOG.
I don't know this comparison is surely exact or not.

I think this comparison need more experiment.

similarity test in video

->https://www.youtube.com/watch?v=rAMMA8AQM_o

->https://www.youtube.com/watch?v=E7SefO1I_E8

#include < opencv2\opencv.hpp>  
#include < stdio.h>  


#ifdef _DEBUG          
#pragma comment(lib, "opencv_core249d.lib")  
#pragma comment(lib, "opencv_imgproc249d.lib")   //MAT processing  
#pragma comment(lib, "opencv_highgui249d.lib")  
#pragma comment(lib, "opencv_objdetect249d.lib")  
#else  
#pragma comment(lib, "opencv_core249.lib")  
#pragma comment(lib, "opencv_imgproc249.lib")  
#pragma comment(lib, "opencv_highgui249.lib")  
#pragma comment(lib, "opencv_objdetect249.lib")  
#endif     

#define M_PI 3.1415

using namespace std;  
using namespace cv;  


Mat get_hogdescriptor_visual_image(Mat& origImg,
                                   vector< float>& descriptorValues,
                                   Size winSize,
                                   Size cellSize,                                   
                                   int scaleFactor,
                                   double viz_factor);

int main()  
{  

 //image load
 Mat img1 = imread("./b1.jpg");
 Mat img2 = imread("./c5.jpg");

 //rgb 2 gray
 Mat img1_gray; 
 cvtColor(img1, img1_gray, CV_RGB2GRAY);

 Mat img2_gray; 
 cvtColor(img2, img2_gray, CV_RGB2GRAY);

 //resize smaller
 Mat r_img1_gray;
 resize(img1_gray, r_img1_gray, Size(64, 8));
 Mat r_img2_gray;
 resize(img2_gray, r_img2_gray, Size(64, 8));


 //extractino hog feature
 HOGDescriptor d1( Size(64,8), Size(8,8), Size(4,4), Size(4,4), 9);
 HOGDescriptor d2( Size(64,8), Size(8,8), Size(4,4), Size(4,4), 9);
 // Size(32,16), //winSize
 // Size(8,8), //blocksize
 // Size(4,4), //blockStride,
 // Size(4,4), //cellSize,
 // 9, //nbins,

 //hog feature compute
 vector< float> descriptorsValues1;
 vector< Point> locations1;
 d1.compute( r_img1_gray, descriptorsValues1, Size(0,0), Size(0,0), locations1);
 vector< float> descriptorsValues2;
 vector< Point> locations2;
 d2.compute( r_img2_gray, descriptorsValues2, Size(0,0), Size(0,0), locations2);

 //hog feature size
 //cout << descriptorsValues1.size() << endl;


 ///////////////////////
 //copy vector to mat  
 //create Mat  
 Mat A(descriptorsValues1.size(),1,CV_32FC1); 
 //copy vector to mat  
 memcpy(A.data,descriptorsValues1.data(),descriptorsValues1.size()*sizeof(float));
 //create Mat  
 Mat B(descriptorsValues2.size(),1,CV_32FC1); 
 //copy vector to mat  
 memcpy(B.data,descriptorsValues2.data(),descriptorsValues2.size()*sizeof(float));


 /////////////////////////
 //sum( sqrt( (A.-B)^2 ) )
 Mat C = A-B;
 C = C.mul(C);
 cv::sqrt(C, C);
 cv::Scalar rr = cv::sum(C);
 float rrr = rr(0);
 cout << "Distance: " << rrr << endl;

 
 //hog visualization
 Mat r1 = get_hogdescriptor_visual_image(r_img1_gray, descriptorsValues1, Size(64,8), Size(4,4), 10, 3);
 Mat r2 = get_hogdescriptor_visual_image(r_img2_gray, descriptorsValues2, Size(64,8), Size(4,4), 10, 3);

 imshow("hog visualization1", r1);
 imshow("hog visualization2", r2);

 waitKey(0);

 return 0;
}

refer to this page http://feelmare.blogspot.kr/2015/02/opencv-hog-descriptor-computation-and.html about the function "get_hogdescriptor_visual_image" in example source code.