ISSUE : Missing packages for ROS2 humble - Gz Garden installation [closed]

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Overall objective : Subscribe to gz.msgs.Image, gz.msgs.Imu, gz.msgs.Odometry and gz.msgs.LaserScan Gazebo Garden SIM topics using ROS2 (I will then use the ROS2-ROS1 bridge to have them in ROS1 to run my VIO code)

Issue : Missing actuator_msgs, gps_msgs and rosidl_pycommon dependencies to colcon build ros_gz_bridge

Setup : Ubuntu Focal 20.04.6 LTS

Steps to reproduce : Follow ROS/Gazebo instructions for Gazebo Garden

• Install gazebo garden from binary
• Install ROS2 Humble from source as requested here.
• Install rosdep rules for Gazebo Garden
• Follow the instructions to compile ros_gz from source in a colcon workspace for ROS humble

Error : When compiling ros_gz from source in my colcon workspace in the last step, running rosdep install -r --from-paths src -i -y --rosdistro humblegives the following error message :

ERROR: the following packages/stacks could not have their rosdep keys resolved
to system dependencies:                                                       
ros_gz_bridge: No definition of [gps_msgs] for OS version [focal]             
ros_gz_sim_demos: No definition of [xacro] for OS version [focal]             
Continuing to install resolvable dependencies...                              
All required rosdeps installed successfully

Subsequently, if I proceed to the next step and run colcon build, I get :

Starting >>> ros_gz_interfaces
Starting >>> ros_gz_sim
[Processing: ros_gz_interfaces, ros_gz_sim]                                                
--- stderr: ros_gz_sim                                                                     
CMake Warning at /usr/share/cmake/gz-cmake3/cmake3/GzFindPackage.cmake:155 (message):
  ign_find_package is deprecated, use gz_find_package instead.
Call Stack (most recent call first):
  CMakeLists.txt:41 (ign_find_package)


---
Finished <<< ros_gz_sim [30.3s]
Finished <<< ros_gz_interfaces [52.6s]                       
Starting >>> ros_gz_bridge
--- stderr: ros_gz_bridge                                
CMake Error at CMakeLists.txt:62 (find_package):
  By not providing "Findactuator_msgs.cmake" in CMAKE_MODULE_PATH this 
  project has asked CMake to find a package configuration file provided by
  "actuator_msgs", but CMake did not find one.

  Could not find a package configuration file provided by "actuator_msgs"
  with any of the following names:

    actuator_msgsConfig.cmake
    actuator_msgs-config.cmake

  Add the installation prefix of "actuator_msgs" to CMAKE_PREFIX_PATH or set
  "actuator_msgs_DIR" to a directory containing one of the above files.  If
  "actuator_msgs" provides a separate development package or SDK, be sure it
  has been installed.


---
Failed   <<< ros_gz_bridge [10.2s, exited with code 1]

Summary: 2 packages finished [1min 3s]
  1 package failed: ros_gz_bridge
  2 packages had stderr output: ros_gz_bridge ros_gz_sim
  3 packages not processed

It says here that

If rosdep fails to install Gazebo libraries and you have not installed them before, please follow Gazebo installation instructions.

But what does that mean? Following those instructions is how I got here in the first place ...

Help would be much appreciated, thank you in advance!

Tanguy