真切的感受到了写代码会大大的加大对原理的理解.代码部分大部分借阅的灰色的石头的博客内容.
#include <iostream>
#include <opencv2/core/core.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/calib3d/calib3d.hpp>
#include <Eigen/Core>
#include <Eigen/Geometry>
#include <g2o/core/base_vertex.h>
#include <g2o/core/base_unary_edge.h>
#include <g2o/core/block_solver.h>
#include <g2o/core/optimization_algorithm_levenberg.h>
#include <g2o/solvers/csparse/linear_solver_csparse.h>
#include <g2o/types/sba/types_six_dof_expmap.h>
#include <chrono>
using namespace std;
using namespace cv;
void find_feature_matches (
const Mat& img_1, const Mat& img_2,
std::vector<KeyPoint>& keypoints_1,
std::vector<KeyPoint>& keypoints_2,
std::vector< DMatch >& matches );
// 像素坐标转相机归一化坐标
Point2d pixel2cam ( const Point2d& p, const Mat& K );
void bundleAdjustment (
const vector<Point3f> points_3d,
const vector<Point2f> points_2d1,
const vector<Point2f> points_2d,
const Mat& K,
Mat& R, Mat& t
);
int main ( int argc, char** argv )
{
if ( argc != 5 )
{
cout<<"usage: pose_estimation_3d2d img1 img2 depth1 depth2"<<endl;
return 1;
}
//-- 读取图像
Mat img_1 = imread ( argv[1], CV_LOAD_IMAGE_COLOR );
Mat img_2 = imread ( argv[2], CV_LOAD_IMAGE_COLOR );
vector<KeyPoint> keypoints_1, keypoints_2;
vector<DMatch> matches;
find_feature_matches ( img_1, img_2, keypoints_1, keypoints_2, matches );
cout<<"一共找到了"<<matches.size() <<"组匹配点"<<endl;
// 建立3D点
Mat d1 = imread ( argv[3], CV_LOAD_IMAGE_UNCHANGED ); // 深度图为16位无符号数,单通道图像
Mat K = ( Mat_<double> ( 3,3 ) << 520.9, 0, 325.1, 0, 521.0, 249.7, 0, 0, 1 );
vector<Point3f> pts_3d;
vector<Point2f> pts_2d;
vector<Point2f> pts_2d1;
for ( DMatch m:matches )
{
//取得审图图中,每个匹配点的深度
ushort d = d1.ptr<unsigned short> (int ( keypoints_1[m.queryIdx].pt.y )) [ int ( keypoints_1[m.queryIdx].pt.x ) ];
if ( d == 0 ) // bad depth
continue;
float dd = d/5000.0;///?????5000从何而来.
Point2d p1 = pixel2cam ( keypoints_1[m.queryIdx].pt, K );//相机归一化坐标
pts_3d.push_back ( Point3f ( p1.x*dd, p1.y*dd, dd ) );
pts_2d.push_back ( keypoints_2[m.trainIdx].pt );//trainIdx是匹配后的描述子索引
//注意这里的keypoint2,因为输入的3D-2D匹配关系是第一张图的3D和第二张图的2D点之间的匹配.
pts_2d1.push_back( keypoints_1[m.trainIdx].pt);
}
cout<<"3d-2d pairs: "<<pts_3d.size() <<endl;
Mat r, t;
solvePnP ( pts_3d, pts_2d, K, Mat(), r, t, false ,SOLVEPNP_EPNP); // 调用OpenCV 的 PnP 求解,可选择EPNP,DLS等方法
Mat R;
cv::Rodrigues ( r, R ); // r为旋转向量形式,用Rodrigues公式转换为矩阵
cout<<"R="<<endl<<R<<endl;
cout<<"t="<<endl<<t<<endl;
cout<<"calling bundle adjustment"<<endl;
bundleAdjustment ( pts_3d, pts_2d1, pts_2d, K, R, t );
}
void find_feature_matches ( const Mat& img_1, const Mat& img_2,
std::vector<KeyPoint>& keypoints_1,
std::vector<KeyPoint>& keypoints_2,
std::vector< DMatch >& matches )
{
//-- 初始化
Mat descriptors_1, descriptors_2;
// used in OpenCV3
Ptr<FeatureDetector> detector = ORB::create();
Ptr<DescriptorExtractor> descriptor = ORB::create();
// use this if you are in OpenCV2
// Ptr<FeatureDetector> detector = FeatureDetector::create ( "ORB" );
// Ptr<DescriptorExtractor> descriptor = DescriptorExtractor::create ( "ORB" );
Ptr<DescriptorMatcher> matcher = DescriptorMatcher::create ( "BruteForce-Hamming" );
//-- 第一步:检测 Oriented FAST 角点位置
detector->detect ( img_1,keypoints_1 );
detector->detect ( img_2,keypoints_2 );
//-- 第二步:根据角点位置计算 BRIEF 描述子
descriptor->compute ( img_1, keypoints_1, descriptors_1 );
descriptor->compute ( img_2, keypoints_2, descriptors_2 );
//-- 第三步:对两幅图像中的BRIEF描述子进行匹配,使用 Hamming 距离
vector<DMatch> match;
// BFMatcher matcher ( NORM_HAMMING );
matcher->match ( descriptors_1, descriptors_2, match );
//-- 第四步:匹配点对筛选
double min_dist=10000, max_dist=0;
//找出所有匹配之间的最小距离和最大距离, 即是最相似的和最不相似的两组点之间的距离
for ( int i = 0; i < descriptors_1.rows; i++ )
{
double dist = match[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 );
//当描述子之间的距离大于两倍的最小距离时,即认为匹配有误.但有时候最小距离会非常小,设置一个经验值30作为下限.
for ( int i = 0; i < descriptors_1.rows; i++ )
{
if ( match[i].distance <= max ( 2*min_dist, 30.0 ) )
{
matches.push_back ( match[i] );
}
}
}
Point2d pixel2cam ( const Point2d& p, const Mat& K )//像素坐标转化为相机坐标
{
return Point2d
(
( p.x - K.at<double> ( 0,2 ) ) / K.at<double> ( 0,0 ),
( p.y - K.at<double> ( 1,2 ) ) / K.at<double> ( 1,1 )
);
}
void bundleAdjustment (
const vector< Point3f > points_3d,
const vector< Point2f > points_2d1,
const vector< Point2f > points_2d,
const Mat& K,
Mat& R, Mat& t )
{
#define PoseVertexNum 2
// 初始化g2o
typedef g2o::BlockSolver< g2o::BlockSolverTraits<6,3> > Block; // pose 维度为 6, landmark 维度为 3
Block::LinearSolverType* linearSolver = new g2o::LinearSolverCSparse<Block::PoseMatrixType>(); // 线性方程求解器
Block* solver_ptr = new Block ( linearSolver ); // 矩阵块求解器
g2o::OptimizationAlgorithmLevenberg* solver = new g2o::OptimizationAlgorithmLevenberg ( solver_ptr );
g2o::SparseOptimizer optimizer;
optimizer.setAlgorithm ( solver );
// vertex
int poseVertexIndex = 0;
Eigen::Matrix3d R_mat;
R_mat <<
R.at<double> ( 0,0 ), R.at<double> ( 0,1 ), R.at<double> ( 0,2 ),
R.at<double> ( 1,0 ), R.at<double> ( 1,1 ), R.at<double> ( 1,2 ),
R.at<double> ( 2,0 ), R.at<double> ( 2,1 ), R.at<double> ( 2,2 );
for (;poseVertexIndex<PoseVertexNum;poseVertexIndex++){
g2o::VertexSE3Expmap* pose =new g2o::VertexSE3Expmap();
pose->setId(poseVertexIndex);
pose->setFixed(poseVertexIndex==0);
if (poseVertexIndex==1){
pose->setEstimate(g2o::SE3Quat(R_mat,Eigen::RowVector3d(t.at<double>(0,0),t.at<double>(1,0),t.at<double>(2,0))));
optimizer.addVertex ( pose );
}
}
int index = PoseVertexNum;
for ( int i=0;i<points_3d.size();i++ ) {
g2o::VertexSBAPointXYZ* point = new g2o::VertexSBAPointXYZ();
point->setId ( index+i);
point->setEstimate ( Eigen::Vector3d ( points_3d[i].x, points_3d[i].y, points_3d[i].z ) );
point->setMarginalized ( true ); // g2o 中必须设置 marg 参见第十讲内容
optimizer.addVertex ( point );
}
// parameter: camera intrinsics
g2o::CameraParameters* camera = new g2o::CameraParameters (
K.at<double> ( 0,0 ), Eigen::Vector2d ( K.at<double> ( 0,2 ), K.at<double> ( 1,2 ) ), 0
);///?????
camera->setId ( 0 );
optimizer.addParameter ( camera );
// edges
// 添加许多边edges: optimizer.addEdge()
index = 1;
for ( int i=0;i<points_2d1.size();i++ )
{
g2o::EdgeProjectXYZ2UV* edge = new g2o::EdgeProjectXYZ2UV();
edge->setId ( index );
///设置链接的顶点,由于这里是二元边,所以每个边都链接两个顶点,用0,1区分。0代表链接point那头,1代表链接pose那头。由于point有好多个,所以需要对应添加,用了index。
edge->setVertex ( 0, dynamic_cast<g2o::VertexSBAPointXYZ*> ( optimizer.vertex ( index +i) ) );
edge->setVertex ( 1, dynamic_cast<g2o::VertexSE3Expmap*>(optimizer.vertex(0)) );
edge->setMeasurement ( Eigen::Vector2d ( points_2d1[i].x, points_2d1[i].y ) );
edge->setParameterId ( 0,0 );
edge->setInformation ( Eigen::Matrix2d::Identity() );
optimizer.addEdge ( edge );
index++;
}
chrono::steady_clock::time_point t1 = chrono::steady_clock::now();
optimizer.setVerbose ( true );
optimizer.initializeOptimization();
optimizer.optimize ( 100 );
chrono::steady_clock::time_point t2 = chrono::steady_clock::now();
chrono::duration<double> time_used = chrono::duration_cast<chrono::duration<double>> ( t2-t1 );
cout<<"optimization costs time: "<<time_used.count() <<" seconds."<<endl;
cout<<endl<<"after optimization:"<<endl;
cout<<"T="<<endl<<Eigen::Isometry3d (dynamic_cast<g2o::VertexSE3Expmap*>(optimizer.vertex(1))->estimate() ).matrix() <<endl;
}