WIP: python API for ROS2

[rhaschke]

Hi @JafarAbdi,

I'm currently working on reenabling the Python API for the ros2 branch of MTC, which you initially disabled when porting to ROS2. Unfortunately, I'm stuck with several issues. One of them is, that the RobotModelLoader cannot access the robot_description_semantic parameter, although it can access robot_description:

[ERROR] [1716476943.051554493] [mtc_tutorial]: Could not find parameter robot_description_semantic and did not receive robot_description_semantic via std_msgs::msg::String subscription within 10.000000 seconds.
Error:   Could not parse the SRDF XML File. Error=XML_ERROR_EMPTY_DOCUMENT ErrorID=13 (0xd) Line number=0
         at line 715 in ./src/model.cpp
[ERROR] [1716476943.053114764] [moveit_rdf_loader.rdf_loader]: Unable to parse SRDF
[ERROR] [1716476943.053302555] [moveit_task_constructor.task]: task pipeline: received invalid robot model
[ERROR] [1716476943.053314726] [moveit_exceptions.exceptions]: Task failed to construct RobotModel
Exception thrown.
Traceback (most recent call last):
  File "/homes/rhaschke/src/ros/src/moveit/mtc/demo/scripts/cartesian.py", line 30, in <module>
    task.loadRobotModel(node)
RuntimeError: Task failed to construct RobotModel

Any idea what is different between these parameters? Shouldn't the rclcpp::Node either be able to access both of them or none?

[rhaschke]

Can any MoveIt2 @moveit/maintainers help on this issue? Any reason why robot_description is found, but robot_description_semantic not?

[henningkayser]

The error is about the subscription which probably succeeds for the robot_description but not for the srdf. I assume none of the original parameters make it through the python bindings or launch system. This sounds oddly familiar with https://github.com/moveit/moveit2/issues/2219 and https://github.com/moveit/moveit2/pull/2393. What config are you working on?

[Abishalini]

When you launch move_group node, did you set this parameter to True? - https://github.com/moveit/moveit2/blob/82ef3fc8dbf6770f309557924634ce0bc4ea6af8/moveit_configs_utils/moveit_configs_utils/launches.py#L216

[rhaschke]

What config are you working on?

I'm running the demo launch file of MTC: ros2 launch demo/launch/demo.launch.py and then an example binary or python script:

• ros2 run moveit_task_constructor_demo cartesian
• python3 demo/scripts/cartesian.py

@Abishalini, your hint resolved the SRDF issue. Thanks! Next issue is that the kinematics parameters are not found: [WARN] [moveit_ros.robot_model_loader]: No kinematics plugins defined. Fill and load kinematics.yaml!

Is there any way to run simple binaries/scripts and pass the corresponding parameters? I don't want to provide a .launch.py for each and every example.

Wouldn't it make sense to fetch those common parameters from the move_group node using ParametersClient classes (see https://answers.ros.org/question/340600/how-to-get-ros2-parameter-hosted-by-another-node)? Did you consider that option?

[MarqRazz]

Next issue is that the kinematics parameters are not found: [WARN] [moveit_ros.robot_model_loader]: No kinematics plugins defined. Fill and load kinematics.yaml!

I've been running into this same issue with some C++ examples I have. I kinda like the idea of getting them from the move_group parameter namespace, but what if my node is built on moveit_cpp? We could provide MTC a namespace that it could search for robot_description_kinematics or it would probably be best if MoveIt published the info on a topic like it does with robot_description_semantic.

What about ompl_planing.yaml and joint_limits? Doesn't MTC need all of the parameters to match the node that is going to execute the planned trajectory?

[matthias88]

I highly appreciate your effort for reenabling the Python API for ROS2. :-) Have you already progressed? Maybe this helps for getting a list of parameters from another node https://answers.ros.org/question/327280/ros2-rclpy-list-parameters-from-node/. If you need anybody for testing (humble, jazzy), I am happy to help.