📢 Project Archive Notice

This repository has been archived and represents the code from the original GRiD paper. Please do not open issues or pull requests here. Active maintenance, updates, and discussions have moved to the new official repository: A2R-Lab/URDFParser

URDFParser

A simple parser libaray for URDF Files. That returns a robot object which can be used to access links, joints, transformation matrices, etc.

Usage:

parser = URDFParser()
robot = parser.parse(urdf_filepath, alpha_tie_breaker = False)

Where the tie breaker is used to order joints with the same parent link.

alpha_tie_breaker=False # URDF ordering used
alpha_tie_breaker=True # Joint name ordering used

Instalation Instructions:

There are 4 required packages beautifulsoup4, lxml, numpy, sympy which can be automatically installed by running:

pip3 install -r requirements.txt

Robot API:

The main API is as follows where XXX can be replaced by:

• joint: a joint object (see API below)
• link: a link object (see API below)
• Xmat: a sympy transformation matrix with one free variable as defined by its joint
• Xmat_Func: a function that returns a numpy matrix when passed a value for the free variable
• Imat: a numpy 6x6 inertia matrix
• S: a numpy 6x1 motion subspace matrix

# A single object by its ID or by its name as defined in the URDF
get_XXX_by_id(lid) # jid for joints 
get_XXX_by_name(name)
# A list of the objects that occur in the given bfs level
get_XXX_by_bfs_level(name)
# A list of the object ordered by their IDs or by their names as defined in the URDF
# Note: The base link/inertia exists at index -1 and so will appear at the beginning of the list
get_XXXs_ordered_by_id(reverse = False)
get_XXXs_ordered_by_name(reverse = False)
# A dictionary of objects by their ID or by their name as defined in the URDF
# Note: The base link/inertia exists at index -1
get_XXXs_dict_by_id()
get_XXXs_dict_by_name()

The API also includes the following functions:

# get the robot name
get_name()
# get the robot type (if applicable)
is_serial_chain()
# get the number of positions and velocities in the robot state as well as numbers of links and joints
# note: links should be joints + 1 when including the base, num_joints = num_pos
#       num_vel = num_pos for fixed base (and is one larger with quaternion)
get_num_pos()
get_num_vel()
get_num_cntrl()
get_num_joints()
get_num_links()
get_num_links_effective() # num_links - 1 (base link is not used in many RBD algorithms when fixed)
# get the max bfs_level
get_max_bfs_level()
# get the IDs at a given bfs level and the bfs level for a given id
get_ids_by_bfs_level(level)
get_bfs_level_by_id(jid)
# get the ID of the parent(s) of a given link(s) by id
get_parent_id(lid)
get_parent_ids(lids)
get_unique_parent_ids(lids) # remove duplicates
# get the full list of parents ordered by id
get_parent_id_array()
# test if there is a repeated parent by ids
has_repeated_parents(jids)
# get the subtree IDs for a given id and total count and test if in a subtree
get_subtree_by_id(jid)
get_total_subtree_count()
get_is_in_subtree_of(jid,jid_of)
# get the ancestor IDs for a given id and total count and test if an ancestor
get_ancestors_by_id(jid)
get_total_ancestor_count()
get_is_ancestor_of(jid,jid_of)
# get all joints that have parent link name as the parent or child link name as the child
get_joints_by_parent_name(parent_name)
get_joints_by_child_name(child_name)
# get the joint that has parent link name as the parent and child link name as the child
get_joint_by_parent_child_name(parent_name,child_name)
# see if the following joints have the same S (useful for codegen)
are_Ss_identical(jids)
# get the velocity damping coefficients
get_damping_by_id(jid)

Joint API:

# get the name, id, and bfs of the joint
get_name()
get_id()
get_bfs_id()
get_bfs_level()
# get the parent and child link name
get_parent()
get_child()
# get the Xmat or Xmat_Func for this joint as defined above
get_transformation_matrix()
get_transformation_matrix_function()
# get the S for this joint as defined above
get_joint_subspace()
# get the velocity damping coefficent for this joint
get_damping()

Link API:

# get the name, id, and bfs of the link
get_name()
get_id()
get_bfs_id()
get_bfs_level()
# get the link's spatial inertia matrix
get_spatial_inertia()