Simulated laser scanner does not respect namespace/prefix

[matthias-mayr]

We are using our MIR in the namespace mir_ and initially had some issues with the navigation in simulation.

More precisely, the laser scan results on /scan are still in the frame front_laser_link rather than mir_front_laser_link and later on in the navigation stack this causes amcl to not publish the transformation between mir_odom_comb and map.

These messages are published by Gazebo using the libgazebo_ros_laser plugin. To work with a prefixed MIR, we had to change the frame configuration of the plugin to this:

<!-- no prefix, plugin always uses a tf_prefix (if none is set it uses robotNamespace) -->
<frameName>${prefix}${link}</frameName>

to make it use the prefix for the frame in the published messages.

Is this, how it's supposed to be or is there another, better way to resolve this?

[mintar]

This was surprisingly tricky so solve. It took me 2 hours to figure out what the heck my colleague meant by the comment above, and more importantly, how to solve it:

<!-- no prefix, plugin always uses a tf_prefix (if none is set it uses robotNamespace) -->

But finally I figured it out. So the problem is that the gazebo_ros_laser plugin does the following:

• If the ROS parameter 'tf_prefix' is set, it prepends the tf_prefix in front of the frameName.
• Otherwise, it prepends the robotNamespace. (see here)

The robotNamespace gets automatically set if you start the spawn_model node inside a namespace. In this case, if we just add ${prefix} in front of the frameName, as you did, we would end up with two namespaces. Since use namespaces in our robot, that would be bad. :)

I have just pushed a couple of commits that allow you to properly set the tf prefix. You can try it like this:

roslaunch mir_gazebo mir_maze_world.launch tf_prefix:=mir

If you want to enable that behavior in your own launch file, just use the xacro arg with the catchy name of prepend_prefix_to_laser_frame, like this:

https://github.com/dfki-ric/mir_robot/blob/ba02a68e7bc0fcdd6942e385c61ca2b33e9d00e4/mir_description/launch/upload_mir_urdf.launch#L6

And as a demonstration of what I mean with the "pushing into namespaces" problem, I've pushed this commit to my personal fork (just for demonstration purposes, I'm not going to merge it):

mintar@c91a543

This is the line where I make sure not to prepend the prefix twice:

mintar@c91a543#diff-025925fc4708d226851d15a6422fb336R43

... because we're operating inside a namespace:

mintar@c91a543#diff-025925fc4708d226851d15a6422fb336R30

Feel free to reopen this issue if it's not solved by those commits.