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## description = This tutorial teaches you how to create a KDL Tree from a [[urdf/XML|URDF]] file
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<<TableOfContents(4)>>

== 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:

{{{#!cplusplus block=action
  #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 ===
 {{{#!cplusplus block=action
   KDL::Tree my_tree;
   if (!kdl_parser::treeFromFile("filename", my_tree)){
      ROS_ERROR("Failed to construct kdl tree");
      return false;
   }
}}}
 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 ===
 {{{#!cplusplus block=action
   KDL::Tree my_tree;
   ros::NodeHandle node;
   std::string robot_desc_string;
   node.param("robot_description", robot_desc_string, std::string());
   if (!kdl_parser::treeFromString(robot_desc_string, my_tree)){
      ROS_ERROR("Failed to construct kdl tree");
      return false;
   }
}}}
=== From an xml element ===
 {{{#!cplusplus block=action
   KDL::Tree my_tree;
   TiXmlDocument xml_doc;
   xml_doc.Parse(xml_string.c_str());
   xml_root = xml_doc.FirstChildElement("robot");
   if (!xml_root){
      ROS_ERROR("Failed to get robot from xml document");
      return false;
   }
   if (!kdl_parser::treeFromXml(xml_root, my_tree)){
      ROS_ERROR("Failed to construct kdl tree");
      return false;
   }
}}}
=== From a URDF model ===
 {{{#!cplusplus block=action
   KDL::Tree my_tree;
   urdf::Model my_model;
   if (!my_model.initXml(....)){
      ROS_ERROR("Failed to parse urdf robot model");
      return false;
   }
   if (!kdl_parser::treeFromUrdfModel(my_model, my_tree)){
      ROS_ERROR("Failed to construct kdl tree");
      return false;
   }
}}}

For more details, take a look at the [[http://www.ros.org/doc/api/kdl_parser/html/namespacekdl__parser.html|API documentation]].


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