Services vs topics #10
Description
I have been developing normal software that uses ROS for a few months now, and one information that was very useful, but that I had to stumble upon many times before getting it, was this :
- topics require a ROS node, and therefore a full ROS environment setup, and the software to follow ROS habits ( only one node_init by process, etc. ) to communicate.
- services are implemented with xmlrpc, and do not require any ROS node or ROS environment setup to communicate, except being able to import the generated python message format.
I think this is an important information that should be somewhere :
How to communicate with running ROS system :
- from inside ros : topics is better ( seems to be ROS devs favorite, and you can even implement service-like behavior on top of them actually : http://wiki.ros.org/rocon_python_comms/Tutorials/indigo/What%20are%20Service%20Pairs%3F )
- from outside ros : service is better : discover the uri (getting the master uri is another topic - see python dynamically setup ros environment #9) and connect (message format import).
I am currently working on a package to bridge different multiprocess architectures ( https://github.com/asmodehn/pyros ) but it is overkill if the robot developers take care of exposing the proper services, and the robot users know how to call these services directly ( from outside ).