while playing with the beta wanted to create a callback on two topics.
In ROS it is possible through the message_filters package e.g.
message_filters::Subscriber image1_sub(nh, “image1”, 1);
message_filters::Subscriber image2_sub(nh, “image2”, 1);
TimeSynchronizer<Image, Image> sync(image1_sub, image2_sub, 10);
sync.registerCallback(boost::bind(&callback, _1, _2));
i don’t know if this is possible in ROS2 yet? I couldn’t find anything in the demos.