OpenCV KNN draw matches - opencv

Question

I'm using KNN to classify images. Now my problem is how to draw the results.
Click here to get the documentation for KNN in OpenCV
I'm using the function find_nearest, which constructor looks like this:
C++: float CvKNearest::find_nearest(const Mat& samples, int k, Mat& results, Mat& neighborResponses, Mat& dists)
Where the parameters are:
samples : Input samples stored by rows. It is a single-precision floating-point matrix of number\_of\_samples \times number\_of\_features size.
k : Number of used nearest neighbors. It must satisfy constraint: k \le CvKNearest::get_max_k().
results : Vector with results of prediction (regression or classification) for each input sample. It is a single-precision floating-point vector with number_of_samples elements.
neighbors : Optional output pointers to the neighbor vectors themselves. It is an array of k*samples->rows pointers.
neighborResponses : Optional output values for corresponding neighbors. It is a single-precision floating-point matrix of number\_of\_samples \times k size.
dist : Optional output distances from the input vectors to the corresponding neighbors. It is a single-precision floating-point matrix of number\_of\_samples \times k size.
A posible implementation would look like this:
#include "ml.h"
#include "highgui.h"
int main( int argc, char** argv )
{
const int K = 10;
int i, j, k, accuracy;
float response;
int train_sample_count = 100;
CvRNG rng_state = cvRNG(-1);
CvMat* trainData = cvCreateMat( train_sample_count, 2, CV_32FC1 );
CvMat* trainClasses = cvCreateMat( train_sample_count, 1, CV_32FC1 );
IplImage* img = cvCreateImage( cvSize( 500, 500 ), 8, 3 );
float _sample[2];
CvMat sample = cvMat( 1, 2, CV_32FC1, _sample );
cvZero( img );
CvMat trainData1, trainData2, trainClasses1, trainClasses2;
// form the training samples
cvGetRows( trainData, &trainData1, 0, train_sample_count/2 );
cvRandArr( &rng_state, &trainData1, CV_RAND_NORMAL, cvScalar(200,200), cvScalar(50,50) );
cvGetRows( trainData, &trainData2, train_sample_count/2, train_sample_count );
cvRandArr( &rng_state, &trainData2, CV_RAND_NORMAL, cvScalar(300,300), cvScalar(50,50) );
cvGetRows( trainClasses, &trainClasses1, 0, train_sample_count/2 );
cvSet( &trainClasses1, cvScalar(1) );
cvGetRows( trainClasses, &trainClasses2, train_sample_count/2, train_sample_count );
cvSet( &trainClasses2, cvScalar(2) );
// learn classifier
CvKNearest knn( trainData, trainClasses, 0, false, K );
CvMat* nearests = cvCreateMat( 1, K, CV_32FC1);
for( i = 0; i < img->height; i++ )
{
for( j = 0; j < img->width; j++ )
{
sample.data.fl[0] = (float)j;
sample.data.fl[1] = (float)i;
// estimate the response and get the neighbors' labels
response = knn.find_nearest(&sample,K,0,0,nearests,0);
// compute the number of neighbors representing the majority
for( k = 0, accuracy = 0; k < K; k++ )
{
if( nearests->data.fl[k] == response)
accuracy++;
}
}
}
Now back to the problem. I want to use the function DrawMatches. Click here to see the description. This function expects its input as DMatch-Type matrix. So as you see Knn.find_nearest does not give me any return of this type. Do you have any suggestion how to convert those?
Thanks in advance!