topic /ir_intensity contains more than one type

[framlin]

Does anybody know, how i can select the type of a topic in rviz2, if a topic hast two types?
The topic /ir_intensity has the types irobot_create_msgs/msg/IrIntensityVector and sensor_msgs/msg/PointCloud and rviz2 is taking the first one instead of the second for the display PointCloud.
How can I tell the create3 to send sensor_msgs/msg/PointCloud-type-messages or rviz2, to display the irobot_create_msgs/msg/IrIntensityVector-data?
Or do I miss the point totally, why rviz2 does not display the /ir_intensity -data?
Thanks in advance

[alsora]

The Create 3 robot publishes data on the /ir_intensity-data topic using only irobot_create_msgs/msg/IrIntensityVector.
ROS does not support to publish messages of different types on the same topic and, in the more recent releases, it would crash right away if you try to do that.

However, the main point is different.
It sounds like you want to display the /ir_intensity-data topic in RViz and unfortunately this is not possible out of the box.
RViz can display only a limited number of topics, i.e. those topics that use message types supported by the RViz plugins.
The irobot_create_msgs/msg/IrIntensityVector, being a "custom" ROS topic developed by iRobot for the Create 3, does not have plugins yet.

You can find here documentation for RViz, which includes instructions on how to write new plugins: https://wiki.ros.org/rviz
It would be a great project if someone would develop a new RViz plugin to display some of the Create 3 topics!

[alsora]

Can you run this command in a terminal and show me the output?

ros2 topic info /ir_intensity --verbose

This should show information about the topic.

[framlin]

root@verdi:~/create3_ws# ros2 topic info /ir_intensity --verbose
Type: irobot_create_msgs/msg/IrIntensityVector

Publisher count: 1

Node name: robot_state
Node namespace: /
Topic type: irobot_create_msgs/msg/IrIntensityVector
Endpoint type: PUBLISHER
GID: 01.10.a6.61.41.f9.b4.95.df.22.5d.41.00.01.b1.03.00.00.00.00.00.00.00.00
QoS profile:
  Reliability: BEST_EFFORT
  Durability: VOLATILE
  Lifespan: 9223372036854775807 nanoseconds
  Deadline: 9223372036854775807 nanoseconds
  Liveliness: AUTOMATIC
  Liveliness lease duration: 9223372036854775807 nanoseconds

Subscription count: 0

Indeed, that looks as if there is only one type.

This is after I have restartet my terminals and the galactic-docker-image.
And now, 'ros2 topic echo /ir_intensity' shows the ir_intensity-data again ... really strange ....

Thank you for your help!

[alsora]

Great, I'm glad it works now.

The explanation I can give is that maybe you had an additional ROS 2 application running on your system and this application was using that other message type you were seeing on that same topic.
An example could also have been trying to publish from ROS 2 command line on the topic.

[framlin]

Thank you very much!
So I assume it was rviz2, that confused did that confusing things

[framlin]

.... and ..... create 3 is really a great toy ;-) ..........