Use values of a callback in another callback
Hello guys,
I need to write a rospy node, which subscribes to two topics and publishes to one topic. I want to work in callback1 with the gathered values of callback2, but I am wondering how this gonna work. The idea is like follows:
init_node
publisher
subscriber(......, callback_laserscan)
subscriber(......, callback_objectDetection)
callback_laserscan:
get angles
get ranges
callback_objectDetection:
get bounding boxes
work with values of callback_laserscan
publish the result to topic
How can I use the values from the laserscan callback function in my other callback function, should I implement a class where I have methods for my subscriber and publisher and save the values of callback_laserscan in a member variable? I've read that rospy is multithreaded, does that mean both functions/methods run simultaneously when a message arrives?
My setup is Ubuntu 16.04 LTS with ROS kinetic.
I appreciate every hint and help
cheesee61
Hi @cheesee61,
Technically the callback is called every time a new message is extracted from the queue. If you want to use the value of a callback in another callback I think about two possible solutions.
However, in both ways I think it is very important that you take into account data races, thus, depending on what you want to do with that data you may want to include a mutex in order to avoid race conditions.
In almost all cases when both messages have
std_msgs/Headerfields, it would be recommended to use message_filters instead of writing something yourself with member variables, etc.Wow, I did not know about the existence of it. That would be more suitable.
Thx to both of you guys, especially @gvdhoorn helped me a lot over the last while, thanks!