cxrandolph's profile - activity

@rrand Well, in this example the callbacks doing the publishing were indeed completing. However, some of the callbacks t

ROS2 Multithreaded executor fails to invoke subscriber callback Problem I have created a simple ROS2 application with a

MultiThreadedExecutor failing to execute callback vs SingleThreadedExecutor Problem I have created a simple ROS2 applic

ROS2 Multithreaded executor fails to invoke subscriber callback Problem I have created a simple ROS2 application with a

ROS2 quietly crashes when running as a forked process Summary I've created a simple process that forks, then launches o

ROS2 quietly crashes when running as a forked process Summary I've created a simple process that forks, then launches o

Context

The Turtlebot3 platform is commonly referenced in ROS as an example robotics application. I was excited to learn about how this project was structured internally, and so I have downloaded it (only for ROS 1, not 2) and decided to run the turtlebot3_fake_node 3D visualization tool RViz as mentioned in this guide.

Problem

Once I got launched the simulator nodes, as well as the teleop-key input processes, I launched rqt_graph in order to check out how the project is structured in terms of ROS nodes, topics, and subscriptions. However, I discovered that there were only a few nodes and topics visible (where are the sensor topics, etc?). The entire robot behavior is encapsulated within the fake node.

Is there another way to get introspection on how turtlebot3 works internally without an extensive review of the source code? I unfortunately do not have access to the real robot either.

Cheers

@gvdhoorn I was under the impression that nodes within ROS typically represented small execution units. So I was expecti

I was under the impression that nodes within ROS typically represented small execution units. So I was expecting to see

Why does RQT Graph have limited insight into Turtlebot3? Context The Turtlebot3 platform is commonly referenced in ROS

Why does RQT Graph have limited insight into Turtlebot3? Context The Turtlebot3 platform is commonly referenced in ROS

Thank you for this! It is very informative. It makes sense that since DDS is supposed to be distributive, assuming it wo

Objective

Running a ROS2 node launches a background process which I imagine is the DDS implementation (FastRTPS). This process is then responsible for forwarding all messages over the middleware to any other ROS2 processes.

I'm trying to find out where exactly this happens. ROS2 is not a single executable, but uses a CLI program to handle commands and then appears to take care of launching the appropriate processes. However, I've not been able to pinpoint where the background process is launched. It may be that the executable node itself forks something when using the rclcpp (or rclpy) API calls.

Does anyone have some quick insight or resources about this? I find that trying to understand the source code of ROS2 is quite difficult because of so many templates and macros and abstract interfaces.

Thank you for this! It is very informative.

Where is DDS forked or exec'd in the ROS2 CLI? Objective Running a ROS2 node launches a background process which I imag

@gbdhoorn Oh yeah thanks. That was a mistake.

Running RCLCPP as a custom package? ROS2 is constructed in much the way the official guides recommend that one builds th

Running RCLCPP as a custom package? ROS2 is constructed in much the way the official guides recommend that one builds th

@tfoote Good call with .bashrc. I've cleared it out, and removed some stuff in /opt/ that was also related to dashing.

I'm interested in working with rclcpp, so I've decided to install ROS2 (Dashing) by building it from source, on a system with a fresh upgrade to Ubuntu 19.10 eoan. I am using this guide from ros.org to do so. However, I simply cannot manage to successfully build ROS2. The following problems I have encountered are:

1. Install development tools and ROS tools: I was unable to succesfully run sudo apt install python3-colcon-common-extensions. It returned with E: Unable to locate package python3-colcon-common-extensions.

   Workaround: I obtained colcon using pip3 install -U colcon-common-extensions. I then added it to my PATH environment variable

2. Install dependencies using rosdep: Running rosdep install --from-paths src --ignore-src --rosdistro dashing -y --skip-keys "console_bridge fastcdr fastrtps libopensplice67 libopensplice69 rti-connext-dds-5.3.1 urdfdom_headers" yielded the following output: ERROR: the following packages/stacks could not have their rosdep keys resolved to system dependencies: rosidl_parser: No definition of [python3-lark-parser] for OS version [eoan]

   I was able to install python3-lark-parser through pip3 however, and hoped that sorted out the problem.

3. Building: Running colcon build --symlink-install yields:

   • Summary: 169 packages finished [13min 11s]
   • 1 package failed: rviz_rendering
   • 5 packages aborted: diagnostic_msgs rclcpp sensor_msgs shape_msgs visualization_msgs
   • 23 packages had stderr output: actionlib_msgs composition_interfaces diagnostic_msgs fastrtps geometry_msgs lifecycle_msgs nav_msgs qt_gui_cpp rcl_interfaces rmw_connext_cpp rmw_connext_shared_cpp rmw_fastrtps_shared_cpp rmw_opensplice_cpp rosidl_generator_py rosidl_typesupport_connext_c rosidl_typesupport_connext_cpp rviz_rendering sensor_msgs std_msgs std_srvs test_msgs tf2_msgs visualization_msgs
   • 96 packages not processed

After this I was unable to do anything to try and repair my installation. I unfortunately feel a bit overwhelmed by the amount of dependencies and what I perceive to be the complexity of the ROS2 build process.

Are there any measures I can take to repair my installation and get ROS2 working?

Okay. Following advice from marguedas for the rosdep workaround, combined with the flag --os=ubuntu:bionic to get around