Converting iOS code to Android, OpenCV

Question

I have Code as following which is working fine in iOS, and i Want to convert that code into Android. If anyone have used openCV library then please help me out.

Code is used for finding smaller image is available in larger image or not, and if available then finding the coordinates of it.

Note that: for android, as SURF is not available in opencv 4.1.2 or higher, so, here i am using opencv 4.1.1(http://garr.dl.sourceforge.net/project/opencvlibrary/opencv-android/2.4.1/OpenCV-2.4.1-android-bin2.tar.bz2)

Code:

-(void)featureDetection:(UIImage*)largerImage withImage:(UIImage*)subImage
{
cv::Mat tempMat1 = [largerImage CVMat];
cv::Mat tempMat2 = [subImage CVMat];

cv::cvtColor(tempMat1, tempMat1, CV_RGB2GRAY);
cv::cvtColor(tempMat2, tempMat2, CV_RGB2GRAY);

if( !tempMat1.data || !tempMat2.data ) {
    return;
}

//-- Step 1: Detect the keypoints using SURF Detector
int minHessian = 25;

cv::SurfFeatureDetector detector( minHessian ); // More Accurate bt take more time..
//cv::FastFeatureDetector detector( minHessian ); //Less Accurate bt take less time..

std::vector<cv::KeyPoint> keypoints_1, keypoints_2;

detector.detect( tempMat1, keypoints_1 );
detector.detect( tempMat2, keypoints_2 );

//-- Step 2: Calculate descriptors (feature vectors)
cv::SurfDescriptorExtractor extractor;

cv::Mat descriptors_1, descriptors_2;

extractor.compute( tempMat1, keypoints_1, descriptors_1 );
extractor.compute( tempMat2, keypoints_2, descriptors_2 );

std::vector<cv::Point2f> obj_corners(4);

//Get the corners from the object
obj_corners[0] = (cvPoint(0,0));
obj_corners[1] = (cvPoint(tempMat2.cols,0));
obj_corners[2] = (cvPoint(tempMat2.cols,tempMat2.rows));
obj_corners[3] = (cvPoint(0, tempMat2.rows));

//-- Step 3: Matching descriptor vectors with a brute force matcher
//cv::BruteForceMatcher < cv::L2<float> > matcher;
cv::FlannBasedMatcher matcher;
//std::vector< cv::DMatch > matches;
std::vector<cv::vector<cv::DMatch > > matches;

std::vector<cv::DMatch > good_matches;
std::vector<cv::Point2f> obj;
std::vector<cv::Point2f> scene;
std::vector<cv::Point2f> scene_corners(4);
cv::Mat H;

matcher.knnMatch( descriptors_2, descriptors_1, matches,2);

for(int i = 0; i < cv::min(tempMat1.rows-1,(int) matches.size()); i++)  {

    if((matches[i][0].distance < 0.6*(matches[i][1].distance)) && ((int) matches[i].size()<=2 && (int) matches[i].size()>0))  {
        good_matches.push_back(matches[i][0]);
    }
}
cv::Mat img_matches;
drawMatches( tempMat2, keypoints_2, tempMat1, keypoints_1, good_matches, img_matches );

NSLog(@"good matches %lu",good_matches.size());

if (good_matches.size() >= 4)  {

     for( int i = 0; i < good_matches.size(); i++ ) {
         //Get the keypoints from the good matches
         obj.push_back( keypoints_2[ good_matches[i].queryIdx ].pt );
         scene.push_back( keypoints_1[ good_matches[i].trainIdx ].pt );
     }

     H = findHomography( obj, scene, CV_RANSAC );

     perspectiveTransform( obj_corners, scene_corners, H);

     NSLog(@"%f %f",scene_corners[0].x,scene_corners[0].y);//This is the value which i Want to find out
     NSLog(@"%f %f",scene_corners[1].x,scene_corners[1].y);
     NSLog(@"%f %f",scene_corners[2].x,scene_corners[2].y);
     NSLog(@"%f %f",scene_corners[3].x,scene_corners[3].y);


     //Draw lines between the corners (the mapped object in the scene image )
     line( tempMat1, scene_corners[0], scene_corners[1], cvScalar(0, 255, 0), 4 );

     line( tempMat1, scene_corners[1], scene_corners[2], cvScalar( 0, 255, 0), 4 );

     line( tempMat1, scene_corners[2], scene_corners[3], cvScalar( 0, 255, 0), 4 );

     line( tempMat1, scene_corners[3], scene_corners[0], cvScalar( 0, 255, 0), 4 );
 }

 // View matching..

 UIImage *resultimage = [UIImage imageWithCVMat:img_matches];
 UIImageView *imageview = [[UIImageView alloc] initWithImage:resultimage];
 imageview.frame = CGRectMake(0, 0, 320, 240);
 [self.view addSubview:imageview];

 // View Result

 UIImage *resultimage2 = [UIImage imageWithCVMat:tempMat1];
 UIImageView *imageview2 = [[UIImageView alloc] initWithImage:resultimage2];
 imageview2.frame = CGRectMake(0, 240, 320, 240);
 [self.view addSubview:imageview2];
}

Answer 1

I got solution to my own question. I have found the answer from question given at Object detection with OpenCV Feature Matching with a threshold/similarity score - Java/C++

with required changes as i have mentioned in that post. check it out.