二维特征点(Features2D)和单映射(Homography)寻找已知物体

#include <stdio.h>
#include <iostream>
#include "opencv2/core/core.hpp"
#include "opencv2/features2d/features2d.hpp"
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/calib3d/calib3d.hpp"
#include <opencv2/nonfree/features2d.hpp>  
#include<opencv2/legacy/legacy.hpp>
using namespace cv;

void readme();

/** @function main */
int main(int argc, char** argv)
{
	/*if (argc != 3)
	{
		readme(); return -1;
	}*/

	Mat img_object = imread("box.png", CV_LOAD_IMAGE_GRAYSCALE);
	Mat img_scene = imread("box_in_scene.png", CV_LOAD_IMAGE_GRAYSCALE);

	if (!img_object.data || !img_scene.data)
	{
		std::cout << " --(!) Error reading images " << std::endl; return -1;
	}

	//-- Step 1: Detect the keypoints using SURF Detector
	int minHessian = 400;

	SurfFeatureDetector detector(minHessian);
	//FastFeatureDetector detector(minHessian)
	
	std::vector<KeyPoint> keypoints_object, keypoints_scene;

	detector.detect(img_object, keypoints_object);
	detector.detect(img_scene, keypoints_scene);

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

	Mat descriptors_object, descriptors_scene;

	extractor.compute(img_object, keypoints_object, descriptors_object);
	extractor.compute(img_scene, keypoints_scene, descriptors_scene);

	//-- Step 3: Matching descriptor vectors using FLANN matcher
	FlannBasedMatcher matcher;
	//BruteForceMatcher< L2<float> > matcher
	std::vector< DMatch > matches;
	matcher.match(descriptors_object, descriptors_scene, matches);

	double max_dist = 0; double min_dist = 100;

	//-- Quick calculation of max and min distances between keypoints
	for (int i = 0; i < descriptors_object.rows; i++)
	{
		double dist = matches[i].distance;
		if (dist < min_dist) min_dist = dist;
		if (dist > max_dist) max_dist = dist;
	}

	printf("-- Max dist : %f \n", max_dist);
	printf("-- Min dist : %f \n", min_dist);

	//-- Draw only "good" matches (i.e. whose distance is less than 3*min_dist )
	std::vector< DMatch > good_matches;

	for (int i = 0; i < descriptors_object.rows; i++)
	{
		if (matches[i].distance < 3 * min_dist)
		{
			good_matches.push_back(matches[i]);
		}
	}

	Mat img_matches;
	drawMatches(img_object, keypoints_object, img_scene, keypoints_scene,
		good_matches, img_matches, Scalar::all(-1), Scalar::all(-1),
		vector<char>(), DrawMatchesFlags::NOT_DRAW_SINGLE_POINTS);

	//-- Localize the object
	std::vector<Point2f> obj;//特征点坐标
	std::vector<Point2f> scene;

	for (int i = 0; i < good_matches.size(); i++)
	{ 
		//-- Get the keypoints from the good matches
		obj.push_back(keypoints_object[good_matches[i].queryIdx].pt);
		scene.push_back(keypoints_scene[good_matches[i].trainIdx].pt);
	}
	//单应性是一个平面到另外一个平面的投影映射
	Mat H = findHomography(obj, scene, CV_RANSAC);/////求解单应性矩阵

	//-- Get the corners from the image_1 ( the object to be "detected" )
	std::vector<Point2f> obj_corners(4);
	obj_corners[0] = cvPoint(0, 0); obj_corners[1] = cvPoint(img_object.cols, 0);
	obj_corners[2] = cvPoint(img_object.cols, img_object.rows); obj_corners[3] = cvPoint(0, img_object.rows);
	std::vector<Point2f> scene_corners(4);

	perspectiveTransform(obj_corners, scene_corners, H);////投影变换将图1的四个角坐标变换到投影坐标（图二坐标）

	//-- Draw lines between the corners (the mapped object in the scene - image_2 )在拼图上画出这四个边，
	line(img_matches, scene_corners[0] + Point2f(img_object.cols, 0), scene_corners[1] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
	line(img_matches, scene_corners[1] + Point2f(img_object.cols, 0), scene_corners[2] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
	line(img_matches, scene_corners[2] + Point2f(img_object.cols, 0), scene_corners[3] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
	line(img_matches, scene_corners[3] + Point2f(img_object.cols, 0), scene_corners[0] + Point2f(img_object.cols, 0), Scalar(0, 255, 0), 4);
	//-- Show detected matches
	imshow("Good Matches & Object detection", img_matches);

	//
	line(img_scene, scene_corners[0] , scene_corners[1] , Scalar( 0), 4);
	line(img_scene, scene_corners[1] , scene_corners[2] , Scalar(0), 4);
	line(img_scene, scene_corners[2], scene_corners[3] , Scalar( 0), 4);
	line(img_scene, scene_corners[3], scene_corners[0] , Scalar( 0), 4);
	imshow("img_scene", img_scene);

	waitKey(0);
	return 0;
}

/** @function readme */
//void readme()
//{
//	std::cout << " Usage: ./SURF_descriptor <img1> <img2>" << std::endl;
//}