1 apt-get update ROS包报错
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://packages.ros.org/ros/ubuntu bionic InRelease: The following signatures were invalid: EXPKEYSIG F42ED6FBAB17C654 Open Robotics <email@example.com> W: Failed to fetch http://packages.ros.org/ros/ubuntu/dists/bionic/InRelease The following signatures were invalid: EXPKEYSIG F42ED6FBAB17C654 Open Robotics <firstname.lastname@example.org> W: Some index files failed to download. They have been ignored, or old ones used instead.
更新ROS apt 仓库使用的公共密钥：
curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc | sudo apt-key add -
sudo curl -sSL https://raw.githubusercontent.com/ros/rosdistro/master/ros.key -o /usr/share/keyrings/ros-archive-keyring.gpg
如果执行以上命令出现gpg: no valid OpenPGP data found.错误，那么需要先执行curl -s https://raw.githubusercontent.com/ros/rosdistro/master/ros.asc（卡住不动就是要翻墙，参考Ubuntu下命令行走代理/终端走代理），然后再执行sudo apt-key add ros.asc即可
CMake Error at /opt/ros/melodic/share/catkin/cmake/catkinConfig.cmake:83 (find_package): Could not find a package configuration file provided by "pcl_ros" with any of the following names: pcl_rosConfig.cmake pcl_ros-config.cmake Add the installation prefix of "pcl_ros" to CMAKE_PREFIX_PATH or set "pcl_ros_DIR" to a directory containing one of the above files. If "pcl_ros" provides a separate development package or SDK, be sure it has been installed.
sudo apt-get install ros-melodic-pcl-ros