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.
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！
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。
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: 529.97Camera.fy: 526.97Camera.cx: 477.44Camera.cy: 261.87Camera.k1: 0.05627Camera.k2: -0.0742Camera.p1: 0.00142Camera.p2: -0.00169Camera.k3: 0.0241Camera.width: 960Camera.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 imageORBextractor.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: 20ORBextractor.minThFAST: 7#--------------------------------------------------------------------------------------------# Viewer Parameters#--------------------------------------------------------------------------------------------Viewer.KeyFrameSize: 0.05Viewer.KeyFrameLineWidth: 1Viewer.GraphLineWidth: 0.9Viewer.PointSize:2Viewer.CameraSize: 0.08Viewer.CameraLineWidth: 3Viewer.ViewpointX: 0Viewer.ViewpointY: -0.7Viewer.ViewpointZ: -1.8Viewer.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 else139 {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 else177 {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 input204 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) const245 {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) const252 {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 for266 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 for285 for(int r = 0; r < inC.rows; ++r)286 {287 const cv::Vec3b288 *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receiver340 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。
本文主要展现了orbslam2在Kinect2下的表现，大致是令人满意的。读者在使用时，请务必注意kinect2的标定，否则很可能出错。
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