REP: 120 Title: Coordinate Frames for Humanoids Robots Version: $Revision: 1 $ Last-Modified: $Date: 2012-01-11 11:53:00 +0200 (Wed, 11 Jan 2012) $ Author: Thomas Moulard Status: Draft Type: Informational Content-Type: text/x-rst Requires: 103, 105 Created: 25-Nov-2011 Post-History: Abstract ======== This REP specifies naming conventions and semantic meaning for coordinate frames of humanoids robots used within ROS. Motivation ========== Developers of packages aimed at humanoids robots need a shared convention for coordinate frames in order to better integrate and re-use software components. The REP 105 [2] already defines frames for mobile bases. This REP both remains compatible with REP 105 [2] and extends it to label other important locations on a humanoid robot such as the gaze (head), left and right wrists, hands and feet. Specification ============= Coordinate Frames ----------------- base_link ''''''''' The coordinate frame called ``base_link`` is rigidly attached to the robot root body. It is recommended to choose the robot waist as its root body. The ``base_link`` can be attached to the root in any arbitrary position or orientation; for every hardware platform there will be a different place on the base that provides an obvious point of reference. Note that REP 103 [1] specifies a preferred orientation for frames. base_footprint '''''''''''''' The ``base_footprint`` is the representation of the robot position on the floor. The floor is usually the level where the supporting leg rests, i.e. z = min(l_sole_z, r_sole_z) where l_sole_z and r_sole_z are the left and right sole height respecitvely. The translation component of the frame should be the barycenter of the feet projections on the floor. With respect to the ``odom`` frame, the roll and pitch angles should be zero and the yaw angle should correspond to the ``base_link`` yaw angle. Rationale: `base_footprint`` provides a fairly stable 2D planar representation of the humanoid even while walking and swaying with the ``base_link``. l_wrist and r_wrist ''''''''''''''''''' The coordinate frame called ``l_wrist`` defines the position and orientation of the left arm regardless of the tool (grasping device for instance) attached to it. The coordinate frame called ``r_wrist`` defines the equivalent frame for the right arm. l_gripper and r_gripper ''''''''''''''''''''''' The coordinate frame called ``l_gripper`` defines the position and orientation of the left arm end effector. If the end effector is a grasping device, the frame should be located at the recommended object grasping location. The frame orientation is defined as X the axis going "toward" the object. Y the main dimension in which the grasping device moves and Z orthogonal to X and Y axes. The coordinate frame called ``r_gripper`` defines the equivalent frame for the right arm. l_ankle and r_ankle ''''''''''''''''''' The coordinate frame called ``l_ankle`` defines the position and orientation of the left leg regardless of the support body geometry. The coordinate frame called ``r_ankle`` defines the equivalent frame for the right leg. l_sole and r_sole ''''''''''''''''' The coordinate frame called ``l_sole`` defines the position and orientation of the left leg support body. The (X,Y) plane of this frame must be coplanar with the support body contact surface. It is recommended to choose the origin as the projection of the support body origin on the contact surface. The Z coordinate of this frame should be on the ground level when standing. The coordinate frame called ``r_sole`` defines the equivalent frame for the right leg. l_toe and r_toe ''''''''''''''' The coordinate frame called ``l_toe`` defines the position and orientation of the left leg toe body. The (X,Y) plan of this frame must be coplanar with the toe body contact surface. It is recommended to choose the origin as the projection of the body center on the contact surface. The coordinate frame called ``r_toe`` defines the equivalent frame for the right leg. gaze '''' The coordinate frame called ``gaze`` defines the head position and orientation. The orientation indicates in which direction the head appears to be looking regardless of any sensors (camera for instance). torso ''''' The coordinate frame called ``torso`` is attached to the lowest body of the model which is a parent of ``l_gripper``, ``r_gripper`` and ``gaze``. map and odom '''''''''''' See REP 105 [1] for ``map`` and ``odom`` frames definition. Frame Hierarchy --------------- - base_link - base_footprint - ... - (l|r)_ankle - (l_r)_sole - (l|r)_toe - ... - torso - ... - gaze - ... - (l|r)_wrist - (l|r)_gripper Frame Authorities ----------------- Unlike most mobile bases, the transformation from ``base_link`` to ``base_footprint`` is not rigid on humanoid robots and is broadcasted by an external node. Exceptions ---------- The scope of potential robotics software is too broad to require all ROS software to follow the guidelines of this REP. However, choosing different conventions should be well justified and well documented. Compliance ========== This REP depends on and is compliant with REP 103 [1] and REP 105 [2]. References ========== .. [1] REP 103, Standard Units of Measure and Coordinate Conventions (http://www.ros.org/reps/rep-0103.html) .. [2] REP 105, Coordinate Frames for Mobile Platforms (http://www.ros.org/reps/rep-0105.html) Copyright ========= This document has been placed in the public domain.