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I want to subscribe to openni's "camera/rgb/camera_info" topic to get the camera matrix. Since the matrix doesn't change, I would like to execute the callback just once. How could I achieve this? Is the only way to unsubscribe? Or is it possible to use a ros service for this?
Regards,
Oier
Since camera_info is published with every image frame, the simplest solution is to subscribe to it. In you message callback: collect the data, then unsubscribe.
It is possible your callback may run a few more times after you unsubscribe. Just to be safe, set a flag when you unsubscribe and return immediately if you get called again.
I know this question has been answered by @joq, but that was quite some time ago.
Not sure when it was added, but I believe that ros::topic::waitForMessage(..) (api docs) is a much more elegant solution when only needing a single message.
This function takes care of everything that @joq suggests, ie: subscribing, waiting for a message and then unsubcribing immediately. The caller does not need to maintain any state him or herself (ie: no flag handling, no additional callbacks to ignore).
See #q270298 for an example that shows how to use ros::topic::waitForMessage(..).
A service is better suited for this indeed but than you probably have to create a subscriber node which advertises this service. Perhaps you can also set a variable after the first time the callback is called that prevents executing of the other callback code.
In rospy, the easiest way is to use (as gvdhoorn suggests):
msg = rospy.wait_for_message('/example_topic', ExampleMsg).
Asked: 2013-05-06 01:44:56 -0500
Seen: 4,330 times
Last updated: May 29 '18
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