ROS2 examples

This example package is meant to explore the possibilities of ROS2 from the point of view of current ROS1 features and how the ROS1 feature translate into the new ROS2 architecture. We investigate the aspects that are currently utilized in MRS UAV System with the intention of a potential future transition.

Meant to be tested on 20.04 Foxy

Minimalistic Examples

Everything is a component. We happily nodelet everything in ROS1, so why otherwise?

• ServiceClientExample - periodically calls a service
  • TODO retrieving result synchronously. Some solutions are available, none work for me within a component
  • TODO slow and irregular publishing (Timer-driven) with multi-threaded executor (looks like the same problem can appear even with single-threaded executor)
• PublisherExample - periodically publishes
  • TODO slow and irregular publishing (Timer-driven) with multi-threaded executor (looks like the same problem can appear even with single-threaded executor)
• ServiceServerExample - getting called, ok
• SubscriberExample - subscribes, ok
• TimerExample - runs multiple timers in parallel
  • TODO timer callbacks are not executed in parallel even with multi-threaded container (with multi-threaded executor, looks like the same problem can appear even with single-threaded executor)
• ParamsExample - load params from yaml and launch file
  • param server callback is hooked up
  • TODO investigate the ros__parameters: namespace, which does not seem to be necessary (and does not work when present)

Running the examples

• tmuxinator session

./tmux/start.sh (change the sourced workspace path in tmux/session.yml)

First ROS2 impressions

• colcon, the build system... is it really the best we have got? I want my catkin back.
  • creates workspace wherever colcon build is called
  • therefore, cannot build in subdirectories
  • no colcon clean, no colcon init
  • overall not much user friendly
  • immediately aliased it to fix those hurdles
  • TODO workspace-wide profiles with custom flags
• Sourcing ROS2 workspace
  • ROS2 sourcing

  source /opt/ros/foxy/setup.zsh
  source ~/ros2_workspace/install/setup.zsh

• if you build ROS2 workspace while ROS1 is sourced, you will need to source ROS1 every time before launching ROS2 programs, otherwise, this error will appear:

[INFO] [launch]: All log files can be found below /home/klaxalk/.ros/log/2021-02-16-09-29-27-258633-klaxalk-desktop2-1671935
[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [component_container_mt-1]: process started with pid [1671949]
[component_container_mt-1] [INFO] [1613464167.606666336] [nmspc1_timer_example]: Load Library: /home/klaxalk/ros2_workspace/install/ros2_examples/lib/libtimer_example.so
[component_container_mt-1] /opt/ros/foxy/lib/rclcpp_components/component_container_mt: symbol lookup error: /home/klaxalk/ros2_workspace/install/ros2_examples/lib/libtimer_example.so: undefined symbol: _ZN12class_loader4impl22AbstractMetaObjectBaseC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES9_S9_
[ERROR] [component_container_mt-1]: process has died [pid 1671949, exit code 127, cmd '/opt/ros/foxy/lib/rclcpp_components/component_container_mt --ros-args -r __node:=nmspc1_timer_example -r __ns:=/'].
[WARNING] [launch]: user interrupted with ctrl-c (SIGINT)
[WARNING] [launch]: user interrupted with ctrl-c (SIGINT) again, ignoring...

• Topic the subscribers and publisher have to have compatible Quality of Service (QoS) settings -- reliable or best effort. For example RViZ is setting different profile (reliable) that is by default (best effort). QoS
• mrs_msgs were ported to ROS2
• ROS bridge installs, compiles, runs (scripts here)
  • TODO check performance and load with images
  • TODO check performance and load high publish rates
• Why are most examples still using main() when everything in ROS2 should be a component (nodelet)?
  • https://index.ros.org/doc/ros2/Tutorials/Composition/
  • "Note: It is still possible to use the node-like style of “writing your own main” but for the common case it is not recommended."
• ComponentContainer
  • try running a component as single node by:

  remap = [('cloud_in', '/livox/lidar')]
  node = Node(package='octomap_server2',
               executable='octomap_server',
               output='screen',
               remappings=remap,
               parameters=[params])
  return LaunchDescription([node])

• seems like the multi-threaded container (with multi-threaded executor) fails to execute callbacks (at least Timer callbacks) in parallel
• multi-threaded composer (with multi-threaded executor) produces very uneven and slow rates of timers, Publishing is slow in Docker with MutliThreadedExecutor #1487 (December, 2020)
• CMakeLists.txt
  • basics are fine
  • TODO building (and using) custom libraries
  • TODO building standalone executable nodelets (should be possible)
• Launch files
  • they are in python now link
  • remapping, params, nodelets
  • TODO connecting to existing component containers (nodelet managers)
  • TODO launch prefixes (e.g., launching with GDB)
• Subscribers - work fine, not a big difference from ROS1
  • TODO still problem with multiple callbacks in parallel?
• Publishers - work fine, not a big difference from ROS1
• Service client
  • it is asynchronous only!!!!
  • how to make it behave synchronously? wrapper (only in standalone node)
• Service server - works fine
• Timers - single timer runs, similarly to ROS1 Timers
  • TODO still problem with multiple timers in parallel, recent (last active 2021/01/15) and related issues Avoid timers to be executed twice in the multithreaded executor #1328 and Allow timers to keep up the intended rate in MultiThreadedExecutor #1516 tells me that it is not settled how they should behave ?!?
  • Looks like there is a problem with the regularity of timer callbacks, can be seen with multi-threaded executor
• Parameters
  • basic params work from yaml and launch
  • Beware! loading an empty yaml file causes a long and cryptic error. Solution: add some unused parameter to the file.
  • Nesting is distinguished by "." in the code (it was "/" in ROS1)
  • TODO test overloading multiple configs over each other
  • TODO test more complex types: lists, matrices, ...
• DRS - has a direct implementation in the default parameters
  • callback hooked to the external change of the parameters works
  • validation of the parameters has to be performed in our code -> we will need a custom wrapper for that, otherwise madness
  • ROS2 rqt_reconfigure is super buggy and wonky, this issue is especially hellish
    • it shows the node's parameters sometimes, seems random
• why is the terminal output monochromatic? I want my colors back...
  • export RCUTILS_COLORIZED_OUTPUT=1
• ROS Time
  • TODO test duration, rate, sleep, wall time vs. sim time (we need sim time for faster/slower than real time simulations)
    • To be able to listen sim time, parameter use_sime_time=1 has to be set individually for every node. PR
• Transformations
  • TODO
  • I really hope that ROS2 will support more than just the TF tree, e.g., an Acyclic graph. We need more parents for a node to allow a robot to being localized within more coordinated systems at a time.
  • What about relativistic transformations? Meaning the frames could have a velocity and, therefore, we could transform a moving object (a ball) from a moving frame (a drone) to a world frame.
• Tests
  • TODO
• Pluginlib
  • TODO
• Actionlib
  • TODO
• Lifecycles (new feature)
  • TODO