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Start using the KDL parser

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:

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

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

   1   #include <kdl_parser/kdl_parser.hpp>
   2 

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 xacro.py `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.