ROS:
rostopic:
rostopic bw 显示主题使用的带宽
rostopic delay 显示带有 header 的主题延迟
rostopic echo 打印消息到屏幕
rostopic find 根据类型查找主题
rostopic hz 显示主题的发布频率
rostopic info 显示主题相关信息
rostopic list 显示所有活动状态下的主题
rostopic pub 将数据发布到主题
rostopic type 打印主题类型
rosmsg show 显示消息描述
rosmsg info 显示消息信息
rosmsg list 列出所有消息
rosmsg md5 显示 md5 加密后的消息
rosmsg package 显示某个功能包下的所有消息
rosmsg packages 列出包含消息的功能包
将rosbag包中的 激光点云数据 转换为pcd数据：
话题名转为pcd，命名是 时间戳.pcd
rosrun pcl_ros pointcloud_to_pcd input:=/rslidar_points ./目录
bag包转为pcd
rosrun pcl_ros bag_to_pcd out_2020-01-24-16-42-05.bag /laser_cloud_surround ./pcd
重命名某topic话题：
rosbag play --clock 2021-10-25-09-02-09.bag /test_cloud:=/points_raw
截取某个时间段的rosbag包，或者过滤话题：参考
1过滤单个topic
rosbag filter input.bag only-tf.bag "topic == '/tf'"
2过滤多个topic
rosbag filter input.bag output.bag "topic == '/velodyne_point_cloud' or topic =='/visensor/imu' or topic == '/visensor/left/image_raw'"
3.根据时间过滤
rosbag filter input.bag output.bag "t.to_sec() <= 1284703931.86"
4.同时过滤topic和时间
rosbag filter input.bag output.bag "topic == '/odometry/gps' and t.to_sec() <= 1284703931.86"
5.多个topic和时间
rosbag filter input.bag output.bag "(topic == '/velodyne_point_cloud' or topic =='/visensor/imu' or topic == '/visensor/left/image_raw') and (t.to_sec() >= 1506117983.884751 and t.to_sec() <= 1506118069.884751)"
编译某个特定包：
catkin_make -DCATKIN_WHITELIST_PACKAGES="ndt_omp"
catkin_make -DCATKIN_WHITELIST_PACKAGES="ndt_omp;lidar_imu_calib"
git clone
使用国内镜像，目前已知Github国内镜像网站有github.com.cnpmjs.org和git.sdut.me。
速度根据各地情况而定，在clone某个项目的时候将github.com替换为github.com.cnpmjs.org即可。
ubuntu访问github
1.打开终端命令行，输入命令：sudo gedit /etc/hosts 打开hosts文件，修改里面的内容如下
127.0.0.1 localhost 127.0.1.1 intasect-HP-Desktop-Pro-G2-MT xxx.xxx.xxx.xxx github.com git 13.250.177.223 github.com # github.com 192.30.253.112 github.com 192.30.253.119 gist.github.com 151.101.100.133 assets-cdn.github.com 151.101.100.133 raw.githubusercontent.com 151.101.100.133 gist.githubusercontent.com 151.101.100.133 cloud.githubusercontent.com 151.101.100.133 camo.githubusercontent.com 151.101.100.133 avatars0.githubusercontent.com 151.101.100.133 avatars1.githubusercontent.com 151.101.100.133 avatars2.githubusercontent.com 151.101.100.133 avatars3.githubusercontent.com 151.101.100.133 avatars4.githubusercontent.com 151.101.100.133 avatars5.githubusercontent.com 151.101.100.133 avatars6.githubusercontent.com 151.101.100.133 avatars7.githubusercontent.com 151.101.100.133 avatars8.githubusercontent.com 185.199.108.153 assets-cdn.github.com 185.199.109.153 assets-cdn.github.com 185.199.110.153 assets-cdn.github.com 185.199.111.153 assets-cdn.github.com 151.101.113.194 github.global.ssl.fastly.net # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters
2.有的同学虽然加入了github的相关ip信息，却还是无法访问，这是因为ubuntu系统的安全性问题，还需要在 127.0.0.1 localhost 后面追加
xxx.xxx.xxx.xxx github.com git
13.250.177.223 github.com
上面的xxx.xxx.xxx.xxx 是本机的ipv4地址 ifconfig， 13.250.177.223 是利用站长工具，获取的github数据库的ipv4地址。
站长工具：http://tool.chinaz.com/dns?type=1&host=&ip=
3.修改完后，点击保存。打开浏览器，输入：https://github.com/ ，能够成功访问啦！
串口：
cloudcompare.ccViewer
cloudcompare.CloudCompare
source ./devel/setup.bash
roslaunch rslidar_sdk start.launch
rosrun imu_parse imu_parse
rostopic record /rslidar_points /imu
创建软链接
1,虚假的软连接 ln -s '文件' '文件'
2,真实的软连接
/usr/share/applications$ sudo vim Mydata.desktop
XMind.desktop [Desktop Entry] Version=1.0 Type=Link Name=XMind Comment=XMind file URL=file:///home/l/beifen/xmind-8-update8-linux/XMind_amd64/ Icon=folder X-Ubuntu-Gettext-Domain=example-content MyCode.desktop [Desktop Entry] Version=1.0 Type=Link Name=MyCode Comment=MyCode file URL=file:///home/l/code Icon=folder X-Ubuntu-Gettext-Domain=example-content