Get robot description from topic in GetUrdfService

[Abishalini]

Description

If robot description is not passed as a parameter to the move_group node, this service will fail.
The robot description will now be acquired from the robot_description topic

[codecov]

Codecov Report

Attention: 29 lines in your changes are missing coverage. Please review.

Comparison is base (d962501) 50.74% compared to head (7db923b) 41.07%.
Report is 5 commits behind head on main.

Files	Patch %	Lines
...default_capabilities/get_group_urdf_capability.cpp	0.00%	23 Missing ⚠️
...nning_scene_monitor/src/planning_scene_monitor.cpp	40.00%	3 Missing ⚠️
.../rdf_loader/include/moveit/rdf_loader/rdf_loader.h	0.00%	2 Missing ⚠️
...py/src/moveit/moveit_ros/moveit_cpp/moveit_cpp.cpp	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2681      +/-   ##
==========================================
- Coverage   50.74%   41.07%   -9.67%     
==========================================
  Files         392      690     +298     
  Lines       32553    56237   +23684     
  Branches        0     7287    +7287     
==========================================
+ Hits        16517    23092    +6575     
- Misses      16036    32982   +16946     
- Partials        0      163     +163     

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[tylerjw]

This all looks good except for the QoS on the subscriber. Set it to transient local to make sure you get a copy of the message if the subscriber starts after the publisher.

[MarqRazz]

Should we make sure the topic robot_description is available and wait for a given amount of time if not?

[Abishalini]

I tried using this rclcpp function to wait for a certain time until we get a message in the robot_description topic. But this causes a timeout error when using get_urdf service. Not sure I'm using it wrong.

I could add a while loop with a timer to check if the full_urdf_string_ variable is set.

Do you have a better solution to this?

[tylerjw]

I thought about this a bit more and because you have a moveit_cpp you should be able to get the URDF string like this and not need to manually handle the subscription.

If you add a function to RDFLoader to get the urdf_string_ value it contains. Maybe name it getUrdfString() -> std::string. Then you can do this:

std::string urdf_string = context_
  ->moveit_cpp_
  ->getPlanningSceneMonitor()
  ->getRobotModelLoader()
  ->getRDFLoader()
  ->getUrdfString();

I know it is ugly, but if you have a moveit_cpp and it is initialized, you should be able to get the string this way, too.

Then you could just add this call to top of the callback for your service and you shouldn't have to subscribe to the topic or read the parameter.

[tylerjw]

It's sort of related; do you mind reviewing this? #2682