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视觉SLAM实战（二）：ORB-SLAM2 with Kinect2

前言

实战系列很久没有更新了。近期拿到了一台不错的Thinkpad和Kinect v2，前两天orbslam2又放出，于是想要在kinect2下尝试一下orb slam。整个过程没有特别多的技术含量，读者可以把它当成一个实验步骤的总结。

ORB-slam

orb-slam是15年出的一个单目SLAM，也可以说是单目中做的非常好的一个实现。另一方面，他的代码也极其清爽，编译十分贴心，十分注重我等程序员的用户体验，受到了广大欢迎。前几天，orb-slam作者推出了orb-slam2，在原来的单目基础上增加了双目和RGBD的接口，尽管地图还是单目常见的稀疏特征点图。于是我们就能通过各种传感器来玩orb-slam啦！这里正巧我手上有一个Kinectv2，咱们就拿它做个实验吧！

博主的系统就不多说了，ubuntu14.04, Thinkpad T450。Kinect2 for xbox.

编译Kinect v2

要在ubuntu下使用Kinect V2，需要做两件事。一是编译Kinectv2的开源驱动libfreenect2，二是使用kinect2_bridge在ROS下采集它的图像。这两者在hitcm的博客中已经说的很清楚了，咱就不罗嗦了。

请参照hitcm的博客安装好libfreenect2和iai_kinect2系列软件：

http://www.cnblogs.com/hitcm/p/5118196.html

iai_kinect2中含有四个模块。我们主要用它的bridge进行图像间的转换。此外，还要使用kinect2_registration进行标定。没标定过的kinect2，深度图和彩色图之间是不保证一一对应的，在做slam时就会出错。所以请务必做好它的标定。好在作者十分良心地写了标定的详细过程，即使像博主这样的小白也能顺利完成标定啦！

kinect2_calibration模块，有详细的标定过程解释：

https://github.com/code-iai/iai_kinect2/tree/master/kinect2_calibration

标定之后呢，会得到kinect2彩色头、深度头、红外头的内参和外参，它们都以（万恶的）yaml模式存储在你的机器内。kinect2_bridge会自动检测你的标定文件，对深度图进行校正。之后slam过程主要使用彩色头的内参哦！同时，你也可以使用kinect2_viewer模块来看获取的点云和kinect2的图像哦！

编译orb-slam2

orb-slam2的github位于：https://github.com/raulmur/ORB_SLAM2 直接clone到本地即可。

这版的orb-slam可以脱离ros编译，不需要事先安装ros。（但是由于我们要用kinect2还是装了ros）它的主要依赖项是opencv2.4, eigen3, dbow2和g2o，另外还有一些我没怎么听说过的UI库：pangolin。其中Dbow2和g2o已经包含在它的Thirdparty文件夹中，不需要另外下载啦！opencv的安装方式参见一起做第一篇。（g2o版本问题一直是个坑）所以，只需要去下载pangolin即可。

pangolin的github： https://github.com/stevenlovegrove/Pangolin 它是一个cmake工程，没什么特别的依赖项，直接下载编译安装即可。

随后，进入orb-slam2的文件夹。作者很贴心的为我们准备了 build.sh 文件，直接运行这个文件即可完成编译。

但愿你也顺利编译成功了。orb-slam作者为我们提供了几个example，包括kitti的双目和tum的单目/rgbd。我们可以参照着它去写自己的输入。如果你只想把orb-slam2作为一个整体的模块，可以直接调用include/System.h文件里定义的SLAM System哦。现在我们就把Kinect2丢给它试试。

在Kinect2上运行orb-slam2

Kinect2的topic一共有三种，含不同的分辨率。其中hd是1920的，qhd是四分之一的960的，而sd是最小的。博主发现sd的效果不理想，而hd的图像又太大了，建议大家使用qhd的920大小啦！在调用orb-slam时，需要把相机参数通过一个yaml来告诉它，所以需要简单写一下你的kinect参数喽。比如像这样：

 %YAML:1.0  #-------------------------------------------------------------------------------------------- # Camera Parameters. Adjust them! #--------------------------------------------------------------------------------------------  # Camera calibration and distortion parameters (OpenCV)  Camera.fx: 529.97 Camera.fy: 526.97 Camera.cx: 477.44 Camera.cy: 261.87  Camera.k1: 0.05627 Camera.k2: -0.0742 Camera.p1: 0.00142 Camera.p2: -0.00169 Camera.k3: 0.0241  Camera.width: 960 Camera.height: 540  # Camera frames per second  Camera.fps: 30.0  # IR projector baseline times fx (aprox.) Camera.bf: 40.0  # Color order of the images (0: BGR, 1: RGB. It is ignored if images are grayscale) Camera.RGB: 1  # Close/Far threshold. Baseline times. ThDepth: 50.0  # Deptmap values factor  DepthMapFactor: 1000.0  #-------------------------------------------------------------------------------------------- # ORB Parameters #--------------------------------------------------------------------------------------------  # ORB Extractor: Number of features per image ORBextractor.nFeatures: 1000  # ORB Extractor: Scale factor between levels in the scale pyramid   ORBextractor.scaleFactor: 1.2  # ORB Extractor: Number of levels in the scale pyramid  ORBextractor.nLevels: 8  # ORB Extractor: Fast threshold # Image is divided in a grid. At each cell FAST are extracted imposing a minimum response. # Firstly we impose iniThFAST. If no corners are detected we impose a lower value minThFAST # You can lower these values if your images have low contrast    ORBextractor.iniThFAST: 20 ORBextractor.minThFAST: 7  #-------------------------------------------------------------------------------------------- # Viewer Parameters #-------------------------------------------------------------------------------------------- Viewer.KeyFrameSize: 0.05 Viewer.KeyFrameLineWidth: 1 Viewer.GraphLineWidth: 0.9 Viewer.PointSize:2 Viewer.CameraSize: 0.08 Viewer.CameraLineWidth: 3 Viewer.ViewpointX: 0 Viewer.ViewpointY: -0.7 Viewer.ViewpointZ: -1.8 Viewer.ViewpointF: 500

ORB部分的参数我们就不用动啦。然后，对kinect2_viewer进行一定程度的改写，加入ORBSLAM，就可以跑起来喽：

   1 #include <stdlib.h>   2 #include <stdio.h>   3 #include <iostream>   4 #include <sstream>   5 #include <string>   6 #include <vector>   7 #include <cmath>   8 #include <mutex>   9 #include <thread>  10 #include <chrono>  11   12 #include <ros/ros.h>  13 #include <ros/spinner.h>  14 #include <sensor_msgs/CameraInfo.h>  15 #include <sensor_msgs/Image.h>  16   17 #include <cv_bridge/cv_bridge.h>  18   19 #include <image_transport/image_transport.h>  20 #include <image_transport/subscriber_filter.h>  21   22 #include <message_filters/subscriber.h>  23 #include <message_filters/synchronizer.h>  24 #include <message_filters/sync_policies/exact_time.h>  25 #include <message_filters/sync_policies/approximate_time.h>  26   27 #include <kinect2_bridge/kinect2_definitions.h>  28   29 #include "orbslam2/System.h"  30   31 class Receiver  32 {  33 public:  34   enum Mode  35   {  36     IMAGE = 0,  37     CLOUD,  38     BOTH  39   };  40   41 private:  42   std::mutex lock;  43   44   const std::string topicColor, topicDepth;  45   const bool useExact, useCompressed;  46   47   bool updateImage, updateCloud;  48   bool save;  49   bool running;  50   size_t frame;  51   const size_t queueSize;  52   53   cv::Mat color, depth;  54   cv::Mat cameraMatrixColor, cameraMatrixDepth;  55   cv::Mat lookupX, lookupY;  56   57   typedef message_filters::sync_policies::ExactTime<sensor_msgs::Image, sensor_msgs::Image, sensor_msgs::CameraInfo, sensor_msgs::CameraInfo> ExactSyncPolicy;  58   typedef message_filters::sync_policies::ApproximateTime<sensor_msgs::Image, sensor_msgs::Image, sensor_msgs::CameraInfo, sensor_msgs::CameraInfo> ApproximateSyncPolicy;  59   60   ros::NodeHandle nh;  61   ros::AsyncSpinner spinner;  62   image_transport::ImageTransport it;  63   image_transport::SubscriberFilter *subImageColor, *subImageDepth;  64   message_filters::Subscriber<sensor_msgs::CameraInfo> *subCameraInfoColor, *subCameraInfoDepth;  65   66   message_filters::Synchronizer<ExactSyncPolicy> *syncExact;  67   message_filters::Synchronizer<ApproximateSyncPolicy> *syncApproximate;  68   69   std::thread imageViewerThread;  70   Mode mode;  71   72   std::ostringstream oss;  73   std::vector<int> params;  74   75   //RGBDSLAM  slam; //the slam object  76   ORB_SLAM2::System* orbslam    =nullptr;  77   78 public:  79   Receiver(const std::string &topicColor, const std::string &topicDepth, const bool useExact, const bool useCompressed)  80     : topicColor(topicColor), topicDepth(topicDepth), useExact(useExact), useCompressed(useCompressed),  81       updateImage(false), updateCloud(false), save(false), running(false), frame(0), queueSize(5),  82       nh("~"), spinner(0), it(nh), mode(CLOUD)  83   {  84     cameraMatrixColor = cv::Mat::zeros(3, 3, CV_64F);  85     cameraMatrixDepth = cv::Mat::zeros(3, 3, CV_64F);  86     params.push_back(cv::IMWRITE_JPEG_QUALITY);  87     params.push_back(100);  88     params.push_back(cv::IMWRITE_PNG_COMPRESSION);  89     params.push_back(1);  90     params.push_back(cv::IMWRITE_PNG_STRATEGY);  91     params.push_back(cv::IMWRITE_PNG_STRATEGY_RLE);  92     params.push_back(0);  93   94     string orbVocFile = "/home/xiang/catkin_ws/src/walle/config/ORBvoc.txt";  95     string orbSetiingsFile = "/home/xiang/catkin_ws/src/walle/config/kinect2_sd.yaml";  96   97     orbslam = new ORB_SLAM2::System( orbVocFile, orbSetiingsFile ,ORB_SLAM2::System::RGBD, true );  98   }  99  100   ~Receiver() 101   { 102       if (orbslam) 103       { 104           orbslam->Shutdown(); 105           delete orbslam; 106       } 107   } 108  109   void run(const Mode mode) 110   { 111     start(mode); 112     stop(); 113   } 114  115   void finish()  116   { 117   } 118 private: 119   void start(const Mode mode) 120   { 121     this->mode = mode; 122     running = true; 123  124     std::string topicCameraInfoColor = topicColor.substr(0, topicColor.rfind('/')) + "/camera_info"; 125     std::string topicCameraInfoDepth = topicDepth.substr(0, topicDepth.rfind('/')) + "/camera_info"; 126  127     image_transport::TransportHints hints(useCompressed ? "compressed" : "raw"); 128     subImageColor = new image_transport::SubscriberFilter(it, topicColor, queueSize, hints); 129     subImageDepth = new image_transport::SubscriberFilter(it, topicDepth, queueSize, hints); 130     subCameraInfoColor = new message_filters::Subscriber<sensor_msgs::CameraInfo>(nh, topicCameraInfoColor, queueSize); 131     subCameraInfoDepth = new message_filters::Subscriber<sensor_msgs::CameraInfo>(nh, topicCameraInfoDepth, queueSize); 132  133     if(useExact) 134     { 135       syncExact = new message_filters::Synchronizer<ExactSyncPolicy>(ExactSyncPolicy(queueSize), *subImageColor, *subImageDepth, *subCameraInfoColor, *subCameraInfoDepth); 136       syncExact->registerCallback(boost::bind(&Receiver::callback, this, _1, _2, _3, _4)); 137     } 138     else 139     { 140       syncApproximate = new message_filters::Synchronizer<ApproximateSyncPolicy>(ApproximateSyncPolicy(queueSize), *subImageColor, *subImageDepth, *subCameraInfoColor, *subCameraInfoDepth); 141       syncApproximate->registerCallback(boost::bind(&Receiver::callback, this, _1, _2, _3, _4)); 142     } 143  144     spinner.start(); 145  146     std::chrono::milliseconds duration(1); 147     while(!updateImage || !updateCloud) 148     { 149       if(!ros::ok()) 150       { 151         return; 152       } 153       std::this_thread::sleep_for(duration); 154     } 155     createLookup(this->color.cols, this->color.rows); 156  157     switch(mode) 158     { 159     case IMAGE: 160       imageViewer(); 161       break; 162     case BOTH: 163       imageViewerThread = std::thread(&Receiver::imageViewer, this); 164       break; 165     } 166   } 167  168   void stop() 169   { 170     spinner.stop(); 171  172     if(useExact) 173     { 174       delete syncExact; 175     } 176     else 177     { 178       delete syncApproximate; 179     } 180  181     delete subImageColor; 182     delete subImageDepth; 183     delete subCameraInfoColor; 184     delete subCameraInfoDepth; 185  186     running = false; 187     if(mode == BOTH) 188     { 189       imageViewerThread.join(); 190     } 191   } 192  193   void callback(const sensor_msgs::Image::ConstPtr imageColor, const sensor_msgs::Image::ConstPtr imageDepth, 194                 const sensor_msgs::CameraInfo::ConstPtr cameraInfoColor, const sensor_msgs::CameraInfo::ConstPtr cameraInfoDepth) 195   { 196     cv::Mat color, depth; 197  198     readCameraInfo(cameraInfoColor, cameraMatrixColor); 199     readCameraInfo(cameraInfoDepth, cameraMatrixDepth); 200     readImage(imageColor, color); 201     readImage(imageDepth, depth); 202  203     // IR image input 204     if(color.type() == CV_16U) 205     { 206       cv::Mat tmp; 207       color.convertTo(tmp, CV_8U, 0.02); 208       cv::cvtColor(tmp, color, CV_GRAY2BGR); 209     } 210  211     lock.lock(); 212     this->color = color; 213     this->depth = depth; 214     updateImage = true; 215     updateCloud = true; 216     lock.unlock(); 217   } 218  219   void imageViewer() 220   { 221     cv::Mat color, depth; 222     for(; running && ros::ok();) 223     { 224       if(updateImage) 225       { 226         lock.lock(); 227         color = this->color; 228         depth = this->depth; 229         updateImage = false; 230         lock.unlock(); 231  232         if (orbslam) 233         { 234             orbslam->TrackRGBD( color, depth, ros::Time::now().toSec() ); 235         } 236       } 237  238     } 239  240     cv::destroyAllWindows(); 241     cv::waitKey(100); 242   } 243  244   void readImage(const sensor_msgs::Image::ConstPtr msgImage, cv::Mat &image) const 245   { 246     cv_bridge::CvImageConstPtr pCvImage; 247     pCvImage = cv_bridge::toCvShare(msgImage, msgImage->encoding); 248     pCvImage->image.copyTo(image); 249   } 250  251   void readCameraInfo(const sensor_msgs::CameraInfo::ConstPtr cameraInfo, cv::Mat &cameraMatrix) const 252   { 253     double *itC = cameraMatrix.ptr<double>(0, 0); 254     for(size_t i = 0; i < 9; ++i, ++itC) 255     { 256       *itC = cameraInfo->K[i]; 257     } 258   } 259  260   void dispDepth(const cv::Mat &in, cv::Mat &out, const float maxValue) 261   { 262     cv::Mat tmp = cv::Mat(in.rows, in.cols, CV_8U); 263     const uint32_t maxInt = 255; 264  265     #pragma omp parallel for 266     for(int r = 0; r < in.rows; ++r) 267     { 268       const uint16_t *itI = in.ptr<uint16_t>(r); 269       uint8_t *itO = tmp.ptr<uint8_t>(r); 270  271       for(int c = 0; c < in.cols; ++c, ++itI, ++itO) 272       { 273         *itO = (uint8_t)std::min((*itI * maxInt / maxValue), 255.0f); 274       } 275     } 276  277     cv::applyColorMap(tmp, out, cv::COLORMAP_JET); 278   } 279  280   void combine(const cv::Mat &inC, const cv::Mat &inD, cv::Mat &out) 281   { 282     out = cv::Mat(inC.rows, inC.cols, CV_8UC3); 283  284     #pragma omp parallel for 285     for(int r = 0; r < inC.rows; ++r) 286     { 287       const cv::Vec3b 288       *itC = inC.ptr<cv::Vec3b>(r), 289        *itD = inD.ptr<cv::Vec3b>(r); 290       cv::Vec3b *itO = out.ptr<cv::Vec3b>(r); 291  292       for(int c = 0; c < inC.cols; ++c, ++itC, ++itD, ++itO) 293       { 294         itO->val[0] = (itC->val[0] + itD->val[0]) >> 1; 295         itO->val[1] = (itC->val[1] + itD->val[1]) >> 1; 296         itO->val[2] = (itC->val[2] + itD->val[2]) >> 1; 297       } 298     } 299   } 300  301  302   void createLookup(size_t width, size_t height) 303   { 304     const float fx = 1.0f / cameraMatrixColor.at<double>(0, 0); 305     const float fy = 1.0f / cameraMatrixColor.at<double>(1, 1); 306     const float cx = cameraMatrixColor.at<double>(0, 2); 307     const float cy = cameraMatrixColor.at<double>(1, 2); 308     float *it; 309  310     lookupY = cv::Mat(1, height, CV_32F); 311     it = lookupY.ptr<float>(); 312     for(size_t r = 0; r < height; ++r, ++it) 313     { 314       *it = (r - cy) * fy; 315     } 316  317     lookupX = cv::Mat(1, width, CV_32F); 318     it = lookupX.ptr<float>(); 319     for(size_t c = 0; c < width; ++c, ++it) 320     { 321       *it = (c - cx) * fx; 322     } 323   } 324 }; 325  326 int main(int argc, char **argv) 327 { 328   ros::init(argc, argv, "kinect2_slam", ros::init_options::AnonymousName); 329  330   if(!ros::ok()) 331   { 332     return 0; 333   } 334   std::string topicColor = "/kinect2/sd/image_color_rect"; 335   std::string topicDepth = "/kinect2/sd/image_depth_rect"; 336   bool useExact = true; 337   bool useCompressed = false; 338   Receiver::Mode mode = Receiver::IMAGE; 339   // 初始化receiver 340   Receiver receiver(topicColor, topicDepth, useExact, useCompressed); 341  342   //OUT_INFO("starting receiver..."); 343   receiver.run(mode); 344  345   receiver.finish(); 346  347   ros::shutdown(); 348  349   return 0; 350 }

编译方面，只要在CMakeLists.txt中加入orb-slam的头文件和库，告诉cmake你想链接它即可。甚至你可以把整个orb-slam放到你的代码目录中一块儿编译，不过我还是简单地把liborb_slam2.so文件和头文件拷了过来而已。

实际的手持kinect2运行效果（由于博客园无法传视频，暂时把百度云当播放器使一使）：http://pan.baidu.com/s/1eRcyW1s （感谢也冬同学友情出演……）

一起做rgbd slam的数据集上效果：http://pan.baidu.com/s/1bocx5s

大体上还是挺理想的。