What Is This?

The demos in this package are designed to showcase how developers can manually compose ROS 2 nodes by defining them separately but combining them in varied process layouts.

These can be done while avoiding code overhauls or performance restrictions.

This package consists of the following ROS 2 nodes:

1. camera_node
2. watermark_node
3. image_view_node
4. image_pipeline_all_in_one
5. two_node_pipeline
6. cyclic_pipeline
7. image_pipeline_with_two_image_view

Through the use of intra-process (as opposed to inter-process) node communication, lower latency and thus higher efficiency is observed for ROS 2 topologies that utilizes this manner of communication.

The improvements in latency reduction are even more pronounced when applied to ROS 2 systems with more complex topologies.

Build

colcon build --packages-up-to intra_process_demo

Run

1. Two Node Pipeline

Run two_node_pipeline via the commands below:

ros2 run intra_process_demo two_node_pipeline

This sets up two nodes, a ROS 2 node that publishes a string with an incremeting integer value, as well as a ROS 2 node that subscribes to print the received string.

2. Cyclic Pipeline

Run cyclic_pipeline via the commands below:

ros2 run intra_process_demo cyclic_pipeline

Similar to the previous, instead of creating a new message for each new iteration, the publisher and subscriber nodes only ever use one message instance. This is achieved by having a cycle in the graph and kickstarting the communication externally by having one of the nodes publish before spinning the executor.

3. Image Pipeline All In One

Please ensure you have a camera connected to your workstation.

image_pipeline_all_in_one consists of 3 nodes, where camera_node publishes a unique_ptr message onto the topic, \image. Subsequently, watermark_node subscribes to the previous, republishes the image after adding a watermark on the topic, \watermarked_image, and the final node, image_view_node, subscribes to this last topic in order to display it for user.

ros2 run intra_process_demo image_pipeline_all_in_one

4. Image Pipeline All Separately

Please ensure you have a camera connected to your workstation.

In direct contrast with the previous, run the following commands in separate terminals to have camera_node, watermark_node and image_view_node all in their own process, utilizing inter-process node communication.

This starts the camera_node ROS 2 node and publishes images captured from your workstation web camera onto a ROS 2 topic labelled /image.

# Open new terminal
ros2 run intra_process_demo camera_node

This starts the watermarked_node ROS 2 node which subscribes to raw images from ROS 2 topic /image, overlays both process ID number and message address on top of the image visually and publishes to ROS 2 topic /watermarked_image.

# Open new terminal
ros2 run intra_process_demo watermarked_node

This starts the image_view_node ROS 2 node which subscribes to /watermarked_image and displays the received images in an OpenCV GUI window.

# Open new terminal
ros2 run intra_process_demo image_view_node

5. Image Pipeline With Two Image Views

Please ensure you have a camera connected to your workstation.

Similar to the Image Pipeline All In One, running image_pipeline_with_two_image_view will display the image process through intra-process communications.

However, it now instantiates 2 image_view_node ROS 2 nodes.

# Open new terminal
ros2 run intra_process_demo image_pipeline_with_two_image_view

Verify

1. Two Node Pipeline

When executed correctly, strings should be printed in the terminal similar to what is shown below:

Published message with value: 0, and address: 0x55B68BCC6F20
 Received message with value: 0, and address: 0x55B68BCC6F20
Published message with value: 1, and address: 0x55B68BCC6F20
 Received message with value: 1, and address: 0x55B68BCC6F20
Published message with value: 2, and address: 0x55B68BCC6F20
 Received message with value: 2, and address: 0x55B68BCC6F20
Published message with value: 3, and address: 0x55B68BCC6F20
 Received message with value: 3, and address: 0x55B68BCC6F20

2. Cyclic Pipeline

When executed correctly, strings should be printed in the terminal similar to what is shown below:

Published first message with value:  42, and address: 0x555E4F029480
Received message with value:         42, and address: 0x555E4F029480
  sleeping for 1 second...
  done.
Incrementing and sending with value: 43, and address: 0x555E4F029480
Received message with value:         43, and address: 0x555E4F029480
  sleeping for 1 second...
  done.
Incrementing and sending with value: 44, and address: 0x555E4F029480
Received message with value:         44, and address: 0x555E4F029480
  sleeping for 1 second...
  done.
Incrementing and sending with value: 45, and address: 0x555E4F029480
Received message with value:         45, and address: 0x555E4F029480
  sleeping for 1 second...

3. Image Pipeline All In One

When executed correctly, an OpenCV GUI window should appear displaying something similar to what is shown below:

Take note how the process_id and Message Pointer Address are all the same, proving that all 3 nodes are in the same process.

4. Image Pipleline All Separately

When executed correctly, an OpenCV GUI window should appear displaying something similar to what is shown below:

Notice how all the process_id and Message Pointer Address are now all different, showing that all nodes are using different processes.

5. Image Pipeline With Two Image Views

When executed correctly, 2 OpenCV GUI window should appear displaying similar to what is show below:

For more details on this implementations, please refer to the references below.

References

1. Intra Process Communication tutorial
2. Intra-process Communications in ROS 2

Changelog for package intra_process_demo

0.29.0 (2023-06-07)

0.28.1 (2023-05-11)

• Fix executable name in README (#618)
• Contributors: Yadunund

0.28.0 (2023-04-27)

0.27.0 (2023-04-13)

• Change all ROS2 -> ROS 2. (#610)
• Contributors: Chris Lalancette

0.26.0 (2023-04-11)

• Added README.md for intra_process_demo (#595)
• Contributors: Gary Bey

0.25.0 (2023-03-01)

0.24.1 (2023-02-24)

0.24.0 (2023-02-14)

• Update the demos to C++17. (#594)
• [rolling] Update maintainers - 2022-11-07 (#589)
• Contributors: Audrow Nash, Chris Lalancette

0.23.0 (2022-11-02)

0.22.0 (2022-09-13)

0.21.0 (2022-04-29)

0.20.1 (2022-04-08)

0.20.0 (2022-03-01)

• Add opencv_imgproc dependency for cv::putText (#554)
• Install includes to include/\${PROJECT_NAME} (#548)
• Contributors: Shane Loretz

0.19.0 (2022-01-14)

• Fix include order and relative paths for cpplint (#551)
• Contributors: Jacob Perron

0.18.0 (2021-12-17)

• Update maintainers to Audrow Nash and Michael Jeronimo (#543)
• Additional fixes for documentation in demos. (#538)
• Contributors: Audrow Nash, Chris Lalancette

0.17.0 (2021-10-18)

• Fixing deprecated subscriber callback warnings (#532)
• Contributors: Abrar Rahman Protyasha

0.16.0 (2021-08-11)

• Revert \"Add type masquerading demos (#482)\" (#520)
• Add type masquerading demos (#482)
• Contributors: Audrow Nash, William Woodall

0.15.0 (2021-05-14)

0.14.2 (2021-04-26)

0.14.1 (2021-04-19)

0.14.0 (2021-04-06)

0.13.0 (2021-03-25)

0.12.1 (2021-03-18)

0.12.0 (2021-01-25)

0.11.0 (2020-12-10)

• Update the package.xml files with the latest Open Robotics maintainers (#466)
• Contributors: Michael Jeronimo

0.10.1 (2020-09-21)

0.10.0 (2020-06-17)

0.9.3 (2020-06-01)

0.9.2 (2020-05-26)

0.9.1 (2020-05-12)

0.9.0 (2020-04-30)

• Fix pendulum_control tests to use stdout stream. (#430)
• Contributors: Chris Lalancette

0.8.4 (2019-11-19)

0.8.3 (2019-11-11)

0.8.2 (2019-11-08)

0.8.1 (2019-10-23)

• Replace ready_fn with ReadyToTest action (#404)
• Contributors: Peter Baughman

0.8.0 (2019-09-26)

0.7.6 (2019-05-30)

0.7.5 (2019-05-29)

• Allow ESC/q/sigint to exit demo (#345)
• Contributors: Dirk Thomas

0.7.4 (2019-05-20)

0.7.3 (2019-05-10)

0.7.2 (2019-05-08)

• changes to avoid deprecated API\'s (#332)
• Corrected publish calls with shared_ptr signature (#327)
• Migrate launch tests to new launch_testing features & API (#318)
• Contributors: Michel Hidalgo, William Woodall, ivanpauno

0.7.1 (2019-04-26)

0.7.0 (2019-04-14)

• Added launch along with launch_testing as test dependencies. (#313)
• Updated for NodeOptions Node constructor. (#308)
• Contributors: Michael Carroll, Michel Hidalgo

0.6.2 (2019-01-15)

• Updated to support OpenCV 2, 3 and 4 (#307)
• Contributors: Jacob Perron

0.6.1 (2018-12-13)

0.6.0 (2018-12-07)

0.5.1 (2018-06-28)

0.5.0 (2018-06-27)

• Updated launch files to account for the \"old launch\" getting renamespaced as launch -> launch.legacy. (#239)
• Contributors: Dirk Thomas, William Woodall