Problem Solving: ERROR: the following packages/stacks could not have their rosdep keys resolvedt appears when Ubuntu installs ROS dependencies

1. Specific issues

The computer hard disk is not enough, so install the hard disk to reinstall the system and ROS, and execute

sudo rosdep init
rosdep update

These two steps went smoothly. Next, some ROS dependencies need to be installed, but the following error is reported:

ERROR: the following packages/stacks could not have their rosdep keys resolved
to system dependencies:
simple_models_description: Cannot locate rosdep definition for [urdf_test]
pmb2_rgbd_sensors: Cannot locate rosdep definition for [openni2_launch]
omni_base_description: Cannot locate rosdep definition for [urdf_test]
pmb2_description: Cannot locate rosdep definition for [urdf_test]
pal_navigation_cfg_pmb2: Cannot locate rosdep definition for [spatio_temporal_voxel_layer]
pal_navigation_cfg_pmb3: Cannot locate rosdep definition for [spatio_temporal_voxel_layer]
pal_navigation_cfg_ari: Cannot locate rosdep definition for [slam_toolbox]
pal_gripper_description: Cannot locate rosdep definition for [urdf_test]
tiago_description: Cannot locate rosdep definition for [urdf_test]
omni_base_laser_sensors: Cannot locate rosdep definition for [ira_laser_tools]
social_navigation_layers: Cannot locate rosdep definition for [people_msgs]
pal_navigation_cfg_tiago: Cannot locate rosdep definition for [spatio_temporal_voxel_layer]
pmb2_laser_sensors: Cannot locate rosdep definition for [depthimage_to_laserscan]
tiago_bringup: Cannot locate rosdep definition for [usb_cam]
tiago_laser_sensors: Cannot locate rosdep definition for [ira_laser_tools]
tiago_rgbd_sensors: Cannot locate rosdep definition for [openni2_launch]
omni_base_bringup: Cannot locate rosdep definition for [twist_mux]
pmb2_bringup: Cannot locate rosdep definition for [twist_mux]
pal_robotiq_controller_configuration_gazebo: Cannot locate rosdep definition for [roboticsgroup_upatras_gazebo_plugins]
pal_navigation_cfg_tiago_dual: Cannot locate rosdep definition for [spatio_temporal_voxel_layer]
four_wheel_steering_controller: Cannot locate rosdep definition for [urdf_geometry_parser]

At first, I wondered whether it was a network problem, a rosdep problem, or a conda environment problem, but none of them were resolved. I even uninstalled and reinstalled rosdep and finally found a solution.

Second, the specific environment

Ubuntu 18.04 + ROS melodic

3. Solutions

In fact, the above problem has nothing to do with the idea mentioned before. It is because many packages were omitted during the installation of ROS. I realized that it was because of the lack of the content in [] in the error report.

So take the first line of error reporting as an example

simple_models_description: Cannot locate rosdep definition for [urdf_test]

To solve the problem with this line, just use

sudo apt-get install ros-melodic-urdf-test

To install, and so on, use all the packages in the box in the error report to use

sudo apt-get install ros-你的ROS版本-包名

Remember, the underscore "_" in the package name in the error report needs to be changed to a dash "-" during installation

After all the installation is complete, re-execute the instructions for installing dependencies

Finally, there is no problem with #All required rosdeps installed successfully