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Hi, I am using flann index to implement image matching. In the first program I create feature cluster Mat including all descriptors of images in the database. Then I use this feature cluster to create Index : flann::Index flannIndex(featurecluster, flann::KDTreeIndexParams(), cvflann::FLANN_DIST_EUCLIDEAN);

Then save the index: flannIndex.save("../../index");

======================================== In another program I am trying to load his index by using: flann::Index flannIndex(featurecluster, flann::SavedIndexParams("../../index"), cvflann::FLANN_DIST_EUCLIDEAN); and then executed knn search flannIndex.knnSearch(srcIMG, indices, dists, knn, flann::SearchParams()); But the system had a warning: OpenCV Error: Assertion failed (query.type() == type && indices.type() == CV_32S && dists.type() == dtype)

I am not sure how to assign correct types to query, indices and dists. And if there is a better way to save and load index please let me know. I really appreciate your help! The following is my code:

// SURF.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/nonfree/nonfree.hpp>
#include <opencv2/legacy/legacy.hpp> 
#include <queue>

#include <time.h> 

using namespace cv;
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
    clock_t begin, end;
    begin = clock();
    /*
        SurfFeatureDector() finds feature point
        SurfDescriptorExtractor() extracts descriptor of images
        @para minHessian , a control parameter of SurfFeatureDetector, controlling the number of feature points
        @para DB_SIZE number of images in database
        @para despSRC descriptor of src img
        @para despDB descriptor of database img
    */
    const int minHessian = 3000;
    const int DB_SIZE = 100;
    SurfFeatureDetector detector(minHessian);
    vector<KeyPoint> keyPoints1, keyPoints2;
    SurfDescriptorExtractor extractor;
    Mat despSRC, despDB;
    Mat srcIMG = imread("../../IMG_DB/IMG_67.jpg");
    if (!srcIMG.data){
        cout << "source img not exsit!" << endl;
        return false;
    }
    detector.detect(srcIMG, keyPoints1);
    extractor.compute(srcIMG, keyPoints1, despSRC);

     //build FLANN index 
    //@para featurecluster all descriptor of database
    Mat featurecluster;

    //@para index_IMG documents the relations between indices and img. eg: input a number of index, it gives back its corresponding img
    vector<int>index_IMG; 
    clock_t timeBegin, timeEnd;
    timeBegin = clock();
    for (int i = 1; i <= DB_SIZE; i++)
    {
        char filename[100];
        sprintf_s(filename, "../../IMG_DB/IMG_%d.jpg", i);
        Mat DB_IMG = imread(filename);
        if (!DB_IMG.data){
            cout << "database img not exsit" << endl;
            return 0;
        }
            detector.detect(DB_IMG, keyPoints2);
            extractor.compute(DB_IMG, keyPoints2, despDB);
            //cout << despDB.rows << endl;
            featurecluster.push_back(despDB);
            for (int j = 0; j < despDB.rows; j++){
                index_IMG.push_back(i);
            }
    }
    timeEnd = clock();
    cout << "database calculate time "<<timeEnd - timeBegin;
    Mat indices;
    Mat dists;
    int knn = 2;
    flann::Index flannIndex(featurecluster, flann::KDTreeIndexParams(), cvflann::FLANN_DIST_EUCLIDEAN);
    //flannIndex.knnSearch(despSRC, indices, dists, knn, flann::SearchParams());
    flannIndex.save("../../hehe");
    flannIndex.knnSearch(despSRC, indices, dists, knn, flann::SearchParams());

    /*
        cout << "featurecluster " << featurecluster.rows << endl;
        cout << "keyPoints1 " << keyPoints1.size() << endl;
        cout << "despSRC " << despSRC.rows << endl;
        cout <<"indices size" <<indices << endl;
        cout << "dists" << dists << endl;
    */
    //implement Lowe optimization and retrieve corresponding img
    float nndrRatio = 0.6f; 
    const int maxMatchImgNum = 20;

    struct ImgFreq{
        int ImgIndex;
        int Freq;
    };
    vector<ImgFreq>imgFreq;
    for (int i = 0; i < indices.rows; i++){
        if (dists.at<float>(i, 0) < dists.at<float>(i ...