rostopic echo complains messages not built, but rosmsg says fine?

Background: I have a fresh container of ros-noetic-base, that I want to have full readability of a ros master elsewhere.

rostopic list works fine, so connection to master is fine
rosmsg info specific/message/type works fine. it gives me full details on the message type
rostopic echo /some/topic FAILS, complaining: ERROR: Cannot load message class for [specific/message/type]. Are your messages built?

How can rosmsg be working fine, but rostopic echo fails like this?

Asked by pbrownrobot on 2023-08-07 15:12:51 UTC

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Answers

Guess I'll answer my own question, in part.

Seems like rostopic requires loading python modules, and so makes use of the things in PYTHONPATH. Whereas rosmsg somehow uses the SOURCE CODE, and so makes use of things in ROS_PACKAGE_PATH

Asked by pbrownrobot on 2023-08-08 10:01:46 UTC