[OpenCV] Feature Matching

得到了杂乱无章的特征点后，要筛选出好的特征点，也就是good matches.

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BruteForceMatcher

FlannBasedMatcher

两者的区别：http://yangshen998.iteye.com/blog/1311575

flann的含义：http://www.opencv.org.cn/opencvdoc/2.3.2/html/doc/tutorials/features2d/feature_flann_matcher/feature_flann_matcher.html

在FLANN特征匹配的基础上，还可以进一步利用Homography映射找出已知物体。

具体来说就是利用findHomography函数利用匹配的关键点找出相应的变换，再利用perspectiveTransform函数映射点群。

Mat H = findHomography( obj, scene, CV_RANSAC );  // 获得了变换 Matrix

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From: http://blog.sina.com.cn/s/blog_821b37de0102uzwb.html

OpenCV里有很多的feature，建立和使用方法也比较杂，现在整理一下避免以后用到。

1、detector

统一的定义方式：

Ptr  detector = FeatureDetector::create("STAR");

"FAST" – FastFeatureDetector

"STAR" – StarFeatureDetector

"SIFT" – SIFT (nonfree module)

"SURF" – SURF (nonfree module)

"ORB" – ORB

"BRISK" – BRISK

"MSER" – MSER

"GFTT" – GoodFeaturesToTrackDetector

"HARRIS" – GoodFeaturesToTrackDetector with Harris detector enabled

"Dense" – DenseFeatureDetector

"SimpleBlob" – SimpleBlobDetector

除了统一定义方式之外，有的可以用它自己的feature名字定义，比如

SurfFeatureDetector detector；

SiftFeatureDetector detector;

FastFeatureDetector detector;

STARFeatureDetector detector;

还有一种统一定义方式：

cv::Ptr  detector2 = cv::Algorithm::create("BRISK");

其中cv::可以去掉。

动态的特征点定义方式：

Ptr detector =

            new DynamicAdaptedFeatureDetector(

            AdjusterAdapter::create("SURF"), 100, 500, 5);

2、Descriptorextractor

统一定义方式：  Ptr extractor=DescriptorExtractor::create("SURF");

"SIFT" – SIFT

"SURF" – SURF

"BRIEF" – BriefDescriptorExtractor

"BRISK" – BRISK

"ORB" – ORB

"FREAK" – FREAK

个别定义方式：Ptr extractor=new SiftDescriptorExtractor;

Ptr extractor =new SurfDescriptorExtractor;

Ptr extractor =new BriefDescriptorExtractor;

其他定义方式：

 SurfDescriptorExtractor extractor;

SiftDescriptorExtractor extractor;

BriefDescriptorExtractor extractor;

其他的一些特征可以直接定义对象并用来detect和extract特征

http://docs.opencv.org/modules/features2d/doc/feature_detection_and_description.html?highlight=brisk#BRISK : public Feature2D

比方说 BRISK  BRISKD(60,4,1.0f);

   BRISKD.create("BRISK");

   BRISKD.detect(object,kp_object);

   BRISKD.compute(object,kp_object,des_object);

3、matcher

统一定义方式 Ptr matcher = DescriptorMatcher::create("FlannBased");

BruteForce (it uses L2 )

BruteForce-L1

BruteForce-Hamming

BruteForce-Hamming(2)

FlannBased

其他定义方式：

BFMatcher matcher(type);

normType – One of NORM_L1, NORM_L2, NORM_HAMMING, NORM_HAMMING2. L1 and L2 norms are preferable choices for SIFT and SURF descriptors, NORM_HAMMING should be used with ORB, BRISK and BRIEF, NORM_HAMMING2 should be used with ORB when WTA_K==3 or 4 (see ORB::ORB constructor description).

FlannBasedMatcher matcher;