Is there a way to load urdf from parameter in ros2?

Question

Hi. Sorry for all mistakes, English is not my native language. In ROS 1 we can use this lines:

urdf::Model urdfModel;
urdfModel.initParam("robot_description")

Is there a way to load robot URDF description from parameter in ROS 2 Foxy? I found initXml(), initFile() and initString() methods and that's all. Maybe I'm looking in the wrong place. Appreciate any help.

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Originally posted by Edvard on ROS Answers with karma: 95 on 2022-10-25

Post score: 0

Answer 1

It seems a bit complicated but I managed to instantiate urdf::Model by following the below steps:

1. Get the value of robot_description as string: This requires extra effort. Remember, ROS 2 does not have a centralized parameter server. So, getting a parameter from another node is tricky. You can read more about the procedure at this link.
2. Use the string as input to build URDF model: We can use initString() method.

Code

// license removed for brevity

#include <urdf/model.h>

#include <chrono>
#include <memory>
#include <rclcpp/rclcpp.hpp>

using namespace std::chrono_literals;

class MinimalPublisher : public rclcpp::Node
{
public:
  MinimalPublisher() : Node("minimal_publisher")
  {
    parameters_client_ = std::make_shared<rclcpp::SyncParametersClient>(this, "/robot_state_publisher");
    while (!parameters_client_->wait_for_service(1s))
    {
      if (!rclcpp::ok())
      {
        RCLCPP_ERROR(this->get_logger(), "Interrupted while waiting for the service. Exiting.");
        rclcpp::shutdown();
      }
      RCLCPP_INFO(this->get_logger(), "Service not available, waiting again...");
    }

    std::string urdf_string;
    auto parameters = parameters_client_->get_parameters({ "robot_description" });
    for (auto& parameter : parameters)
    {
      if (parameter.get_name() == "robot_description")
      {
        urdf_string = parameter.value_to_string();
        break;
      }
    }

    urdf::Model urdfModel;
    urdfModel.initString(urdf_string);
    RCLCPP_INFO_STREAM(this->get_logger(), "Name:" << urdfModel.getName());
  }

private:
  std::shared_ptr<rclcpp::SyncParametersClient> parameters_client_;
};

int main(int argc, char* argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalPublisher>());
  rclcpp::shutdown();
  return 0;
}

Run

1. First, I published a URDF using urdf_tutorial. Please see the command below:

   ravi@dell:~$ ros2 launch urdf_tutorial display.launch.py model:=/opt/ros/foxy/share/urdf_tutorial/urdf/06-flexible.urdf
   

2. Next, I confirmed that the robot_description is available as shown below:

   ravi@dell:~$ ros2 param list
   /joint_state_publisher:
     delta
     publish_default_efforts
     publish_default_positions
     publish_default_velocities
     rate
     source_list
     use_mimic_tags
     use_sim_time
     use_smallest_joint_limits
   /robot_state_publisher:
     frame_prefix
     ignore_timestamp
     publish_frequency
     robot_description
     use_sim_time
     use_tf_static
   /rviz2:
     use_sim_time
   

3. Finally, I executed my node which prints URDF model name

   ravi@dell:~/ros2_ws$ ros2 run  examples_rclcpp_minimal_publisher publisher_member_function 
   Parsing robot urdf xml string.
   [INFO] [1666688084.856405837] [minimal_publisher]: Name:visual
   

4. Just for sake of completeness, below is the robot name queried from the terminal:

   ravi@dell:~$ ros2 param get /robot_state_publisher robot_description | grep robot
   <robot name="visual">
   </robot>
   

---

Originally posted by ravijoshi with karma: 1744 on 2022-10-25

This answer was ACCEPTED on the original site

Post score: 3

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Original comments

Comment by Edvard on 2022-10-25:
Thank you so much for you time and help!

Comment by RobotDreams on 2022-10-27:
Is your example code on GitHub somewhere? I want to launch robot state and joint publishers on my robot (not on the Remote Desktop), passing path to the URDF file as a param to the launcher. It seems like your answer is needed for my situation.

Comment by ravijoshi on 2022-10-27:
@RobotDreams: I am out of work now! Give me a day or two, I will upload the complete package to GitHub.

Comment by ravijoshi on 2022-10-28:
@RobotDreams : Here you go: ravijo/minimal_publisher