Keypoint matching just works two times...? (java opencv) -

i have strange problem. i'm using code detect image in 1 (java opencv):

updated code:

public void startrecognition() {     //load images, want find img_object in img_scene     mat img_scene = highgui.imread("d:/opencvws/imagerecognition/src/main/resources/ascene.jpg");     mat img_object = highgui.imread("d:/opencvws/imagerecognition/src/main/resources/aobj1.jpg");     run++;     system.out.println("run no: " + run);      //init detector     featuredetector detector = featuredetector.create(featuredetector.surf);      //keypoint detection both images (keyponts_scene img_scene, keypoint_object img_object)     matofkeypoint keypoints_object = new matofkeypoint();     matofkeypoint keypoints_scene  = new matofkeypoint();     detector.detect(img_object, keypoints_object);     detector.detect(img_scene, keypoints_scene);     system.out.println("ok: " + keypoints_object.total());     system.out.println("sk: " + keypoints_scene.total());      //extractor init     descriptorextractor extractor = descriptorextractor.create(2); //2 = surf;     mat descriptor_object = new mat();     mat descriptor_scene = new mat() ;     //compute descriptors     extractor.compute(img_object, keypoints_object, descriptor_object);     extractor.compute(img_scene, keypoints_scene, descriptor_scene);      //init matcher     descriptormatcher matcher = descriptormatcher.create(descriptormatcher.flannbased); // 1 = flannbased     matcher.clear();     matofdmatch matches = new matofdmatch();      //match both descriptors     matcher.match(descriptor_object, descriptor_scene, matches);     list<dmatch> matcheslist = matches.tolist();      //calc min/max dist     double max_dist = 0.0;     double min_dist = 100.0;     for(int = 0; < descriptor_object.rows(); i++){         double dist = (double) matcheslist.get(i).distance;         if(dist < min_dist) min_dist = dist;         if(dist > max_dist) max_dist = dist;     }      //filter matches     linkedlist<dmatch> good_matches = new linkedlist<dmatch>();     matofdmatch gm = new matofdmatch();      //good match = distance > 2*min_distance ==> put them in list     for(int = 0; < descriptor_object.rows(); i++){         if(matcheslist.get(i).distance < 2*min_dist){             good_matches.addlast(matcheslist.get(i));         }     }     //list -> mat     gm.fromlist(good_matches);      //mat resulting image     mat img_matches = new mat();      //filter keypoints (use matches); first in list, iterate, afterwards ==> mat     linkedlist<point> objlist = new linkedlist<point>();     linkedlist<point> scenelist = new linkedlist<point>();      list<keypoint> keypoints_objectlist = keypoints_object.tolist();     list<keypoint> keypoints_scenelist = keypoints_scene.tolist();      for(int = 0; i<good_matches.size(); i++){         objlist.addlast(keypoints_objectlist.get(good_matches.get(i).queryidx).pt);         scenelist.addlast(keypoints_scenelist.get(good_matches.get(i).trainidx).pt);     }      matofpoint2f obj = new matofpoint2f();     obj.fromlist(objlist);      matofpoint2f scene = new matofpoint2f();     scene.fromlist(scenelist);      //calc transformation matrix; method = 8 (ransac) ransacreprojthreshold=3     mat hg = calib3d.findhomography(obj, scene, 8,3);      //init corners     mat obj_corners = new mat(4,1,cvtype.cv_32fc2);     mat scene_corners = new mat(4,1,cvtype.cv_32fc2);     //obj     obj_corners.put(0, 0, new double[] {0,0});     obj_corners.put(1, 0, new double[] {img_object.cols(),0});     obj_corners.put(2, 0, new double[] {img_object.cols(),img_object.rows()});     obj_corners.put(3, 0, new double[] {0,img_object.rows()});      //transform obj corners scene_img (stored in scene_corners)     core.perspectivetransform(obj_corners,scene_corners, hg);      //move points img_obg width right fit matching image     point p1 = new point(scene_corners.get(0,0)[0]+img_object.cols(), scene_corners.get(0,0)[1]);     point p2 = new point(scene_corners.get(1,0)[0]+img_object.cols(), scene_corners.get(1,0)[1]);     point p3 = new point(scene_corners.get(2,0)[0]+img_object.cols(), scene_corners.get(2,0)[1]);     point p4 = new point(scene_corners.get(3,0)[0]+img_object.cols(), scene_corners.get(3,0)[1]);      //create matching image     features2d.drawmatches(             img_object,             keypoints_object,              img_scene,             keypoints_scene,              gm,              img_matches);     //draw lines matching image     core.line(img_matches, p1 , p2, new scalar(0, 255, 0),4);     core.line(img_matches, p2, p3, new scalar(0, 255, 0),4);     core.line(img_matches, p3, p4, new scalar(0, 255, 0),4);     core.line(img_matches, p4, p1, new scalar(0, 255, 0),4);       // resizing...     mat resizeimage = new mat();     size sz = new size(1200, 1000);     imgproc.resize(img_matches, img_matches, sz);     panel1.setimagewithmat(img_matches);      frame1.repaint();      //tried prevent old references mix new calculation      matcher.clear();     img_matches = new mat();     img_object = new mat();     img_scene = new mat();     keypoints_object = new matofkeypoint();     keypoints_scene = new matofkeypoint();     hg = new mat(); } 

if run startrecognition methode twice (the opencv library loaded @ startup) in running application same result both recognitions. third try detects other keypoints , calculates transformation matrix (hg). examples:

after 2nd try:

after 3rd:

can explain why? or tell me how prevent it? when restart whole program, again detect 2 times correct , afterwards varying. after several tries again calculate correct hg (from first , seceond try). can't figure out why happending.

thanks in advance

gemorra