Ros Api

Provided Functionality

The ROS API provided by the rdl_ros_tools package provides a ROS service interface for performing a number of kinematic operations such as coordinate transforms for twists, wrenches, 3D vectors, and points. There are a number of other services provided for computing other quantities that are often useful in robotics. Below each service will be described in detail. In order to not duplicate documentation, this page will not go into detail on the definition of a twist, etc. For this information please look at the documentation for the rdl_dynamics package or refer to the book Rigid Body Dynamics Algorithms by Roy Featherstone.

Kinematics Service API

The rdl_kinematics_interface node is a ROS node that provides ROS services for doing common kinematics operations such as frame changes, computing twsts, etc.

Prerequisits

The following are necessary for up-to-date, kinematically correct results from the rdl_kinematics_interface node,

• message(s) containing the full state of the robot are being published. Note that the order of the elements in the robot state message is critical. The order must match the RDL model joint order
• A valid URDF for your robot is required and will be consumed by the rdl_kinematics_interface node via rosparam

By default, the node will look at rdl_kinematics_interface/robot_description for an urdf string from which it will build a RobotDynamics::Model object for doing kinematic operations. The rdl_kinematics_interface node subscribes to the following topics for updating the state of the robot,

• State of the joints: rdl_kinematics_interface/joint_states
• Joint and Floating Base State: Full state including joint states and floating base odometry(floating base robots only): rdl_kinematics_interface/robot_state

The following list details the services provided by this node and a brief description of the provided functionality,

• change_frame_point: Change the reference frame a point is expressed in
• change_frame_point_array: Change the reference frame an array of points are expressed in
• change_frame_3dvector: Change the reference frame a 3d vector is expressed in
• change_frame_3dvector_array: Change the reference frame an array of 3d vectors are expressed in
• change_frame_wrench: Change the reference frame a wrench is expressed in
• change_frame_wrench_array: Change the reference frame an array of wrenches is expressed in
• change_frame_twist: Change the reference frame a twist is expressed in
• change_frame_twist_array: Change the reference frame an array of twists are expressed in
• get_twist: Compute a twist
• get_transform: Compute a spatial transform
• get_robot_com: Get a robots center of mass position and velocity
• get_body_grav_wrench: Get the gravity wrench for a given body

If no remapping is desired and you have the appropriate rosparam parameters set, you may run this node by running the following command in the console,

rosrun rdl_ros_tools rdl_kinematics_interface