Note: This tutorial assumes you have already created your own URDF file or that you are working with the existing PR2 URDF file.
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Start using the KDL parser

Description: This tutorial teaches you how to create a KDL Tree from a URDF file

Tutorial Level: BEGINNER

Building the KDL parser

 $ rosdep install kdl_parser

This will install all the external dependencies for the kdl_parser. To build the package, run:

 $ rosmake kdl_parser

Using in your code

First, add the KDL parser as a dependency to your package.xml (in ROS fuerte or earlier it's manifest.xml) file:

    <build_depend package="kdl_parser" />
    <run_depend package="kdl_parser" />

To start using the KDL parser in your C++ code, include the following file:

   1   #include <kdl_parser/kdl_parser.hpp>

Now there are different ways to proceed. You can construct a KDL tree from a urdf in various forms:

From a file

  •    1    KDL::Tree my_tree;
       2    if (!kdl_parser::treeFromFile("filename", my_tree)){
       3       ROS_ERROR("Failed to construct kdl tree");
       4       return false;
       5    }
    To create the PR2 URDF file, run the following command:
     $ rosrun xacro `rospack find pr2_description`/robots/pr2.urdf.xacro > pr2.urdf

From the parameter server

  •    1    KDL::Tree my_tree;
       2    ros::NodeHandle node;
       3    std::string robot_desc_string;
       4    node.param("robot_description", robot_desc_string, std::string());
       5    if (!kdl_parser::treeFromString(robot_desc_string, my_tree)){
       6       ROS_ERROR("Failed to construct kdl tree");
       7       return false;
       8    }

From an xml element

  •    1    KDL::Tree my_tree;
       2    TiXmlDocument xml_doc;
       3    xml_doc.Parse(xml_string.c_str());
       4    xml_root = xml_doc.FirstChildElement("robot");
       5    if (!xml_root){
       6       ROS_ERROR("Failed to get robot from xml document");
       7       return false;
       8    }
       9    if (!kdl_parser::treeFromXml(xml_root, my_tree)){
      10       ROS_ERROR("Failed to construct kdl tree");
      11       return false;
      12    }

From a URDF model

  •    1    KDL::Tree my_tree;
       2    urdf::Model my_model;
       3    if (!my_model.initXml(....)){
       4       ROS_ERROR("Failed to parse urdf robot model");
       5       return false;
       6    }
       7    if (!kdl_parser::treeFromUrdfModel(my_model, my_tree)){
       8       ROS_ERROR("Failed to construct kdl tree");
       9       return false;
      10    }

For more details, take a look at the API documentation.

Wiki: kdl_parser/Tutorials/Start using the KDL parser (last edited 2017-06-02 18:29:06 by DaveKotfis)