ORB_SLAM2的ROS入门1¶

编译ROS节点¶

首先编译以下节点：mono, monoAR, stereo and RGB-D

添加节点的源码路径到 ROS_PACKAGE_PATH 中，打开文件 .bashrc 并将如下内容添加到末尾，这里要将其中的 PATH/ORB_SLAM2 替换成你自己的源码路径，并确保以下内容在文件的 source /opt/ros/melodic/setup.bash 之后，即

编辑文件
```
gedit ~/.bashrc
```
追加以下内容
```
source /opt/ros/melodic/setup.bash
export ROS_PACKAGE_PATH=${ROS_PACKAGE_PATH}:PATH/ORB_SLAM2/Examples/ROS
```
执行 source ~/.bashrc 使上述配置生效
执行源码目录下的 build_ros.sh 脚本
```
chmod +x build_ros.sh
./build_ros.sh
```
在Ubuntu18.04之前的系统上没有问题，但是在Ubuntu18.04及以后的系统上，会出现编译报错，先解决保存问题，重新编译即可。

错误处理¶

如果运行 build_ros.sh 报出如下错误

/usr/bin/ld: CMakeFiles/Stereo.dir/src/ros_stereo.cc.o: undefined reference to symbol '_ZN5boost6system15system_categoryEv'
/usr/lib/x86_64-linux-gnu/libboost_system.so: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
CMakeFiles/Stereo.dir/build.make:217: recipe for target '../Stereo' failed
make[2]: *** [../Stereo] Error 1
CMakeFiles/Makefile2:131: recipe for target 'CMakeFiles/Stereo.dir/all' failed
make[1]: *** [CMakeFiles/Stereo.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

确保boost环境已安装

sudo apt-get install libboost-dev libboost-thread-dev libboost-filesystem-dev

打开 Examples/ROS/ORB_SLAM2/CMakeLists.txt 并在如下位置添加一行 lboost_system

set(LIBS 
${OpenCV_LIBS} 
${EIGEN3_LIBS}
${Pangolin_LIBRARIES}
${PROJECT_SOURCE_DIR}/../../../Thirdparty/DBoW2/lib/libDBoW2.so
${PROJECT_SOURCE_DIR}/../../../Thirdparty/g2o/lib/libg2o.so
${PROJECT_SOURCE_DIR}/../../../lib/libORB_SLAM2.so
-lboost_system
)

修改保存并重新编译即可

./build_ros.sh

运行节点¶

运行如下节点之前，我们要先开启相机设备节点，保证有相机数据发布在 /camera/image_raw 话题，这样我们才能看到图像内容并进行建图和定位。

单目案例

rosrun ORB_SLAM2 Mono Vocabulary/ORBvoc.txt Examples/ROS/ORB_SLAM2/astra.yaml

单目AR案例

rosrun ORB_SLAM2 MonoAR Vocabulary/ORBvoc.txt Examples/ROS/ORB_SLAM2/astra.yaml

由于是我们实时获取的深度数据，此时深度数据缩放因数DepthMapFactor要确保为1.0。

则我们把原来的 ./Examples/ROS/ORB_SLAM2/Asus.yaml 复制一份为 ./Examples/ROS/ORB_SLAM2/astra.yaml 。并且主要要修改以下四个值

Camera.fx
Camera.fy
Camera.cx
Camera.cy

这四个值实际上是通过相机标定得来的，这个在相机相关章节会有原理讲解及实现。

Astra奥比中光相机的 astra.yaml 参考配置文件如下：

%YAML:1.0

#--------------------------------------------------------------------------------------------
# Camera Parameters. Adjust them!
#--------------------------------------------------------------------------------------------

# Camera calibration and distortion parameters (OpenCV) 
Camera.fx: 577.54679
Camera.fy: 578.63325
Camera.cx: 310.24326
Camera.cy: 253.65539

Camera.k1: 0.0
Camera.k2: 0.0
Camera.p1: 0.0
Camera.p2: 0.0

Camera.width: 640
Camera.height: 480

# 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: 40.0

# Deptmap values factor
DepthMapFactor: 1.0

#--------------------------------------------------------------------------------------------
# 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