pytransform3d.urdf.UrdfTransformManager#

class pytransform3d.urdf.UrdfTransformManager(strict_check=True, check=True)[source]#

Bases: TransformManager

Transformation manager that can load URDF files.

The Unified Robot Description Format (URDF) [1] is the most common format to describe kinematic and dynamic properties of robots [2]. This transformation manager allows to set the joint configurations of a robot loaded from a URDF file and provides an interface to its geometric and visual representation.

Warning

Note that this module requires the Python package lxml.

Note

Joint angles must be given in radians.

Parameters:

strict_checkbool, optional (default: True): Raise a ValueError if the transformation matrix is not numerically close enough to a real transformation matrix. Otherwise we print a warning.
checkbool, optional (default: True): Check if transformation matrices are valid and requested nodes exist, which might significantly slow down some operations.

References

[1]

ROS Wiki: urdf, http://wiki.ros.org/urdf

[2]

Tola, D., Corke, P. (2023). Understanding URDF: A Dataset and Analysis. In IEEE Robotics and Automation Letters 9(5), pp. 4479-4486, doi: 10.1109/LRA.2024.3381482. https://arxiv.org/abs/2308.00514

__init__(strict_check=True, check=True)[source]#

Methods

`__init__`([strict_check, check])
`add_joint`(joint_name, from_frame, to_frame, ...)	Add joint.
`add_transform`(from_frame, to_frame, A2B)	Register a transformation.
`check_consistency`()	Check consistency of the known transformations.
`connected_components`()	Get number of connected components.
`from_dict`(tm_dict)	Create transform manager from dict.
`get_joint_limits`(joint_name)	Get limits of a joint.
`get_transform`(from_frame, to_frame)	Request a transformation.
`has_frame`(frame)	Check if frame has been registered.
`load_urdf`(urdf_xml[, mesh_path, package_dir])	Load URDF file into transformation manager.
`plot_collision_objects`(frame[, ax, ax_s, ...])	Plot all collision objects in a given reference frame.
`plot_connections_in`(frame[, ax, ax_s, whitelist])	Plot direct frame connections in a given reference frame.
`plot_frames_in`(frame[, ax, s, ax_s, ...])	Plot all frames in a given reference frame.
`plot_visuals`(frame[, ax, ax_s, wireframe, ...])	Plot all visuals in a given reference frame.
`remove_frame`(frame)	Remove a frame (node) from the graph.
`remove_transform`(from_frame, to_frame)	Remove a transformation.
`set_joint`(joint_name, value)	Set joint position.
`set_transform_manager_state`(tm_dict)	Set state of transform manager from dict.
`to_dict`()	Convert the transform manager to a dict that is serializable.
`write_png`(filename[, prog])	Create PNG from dot graph of the transformations.

Attributes

transforms

Rigid transformations between nodes.

add_joint(joint_name, from_frame, to_frame, child2parent, axis, limits=(-inf, inf), joint_type='revolute')[source]#

Add joint.

Parameters:

joint_namestr: Name of the joint
from_frameHashable: Child link of the joint
to_frameHashable: Parent link of the joint
child2parentarray-like, shape (4, 4): Transformation from child to parent
axisarray-like, shape (3,): Rotation axis of the joint (defined in the child frame)
limitspair of float, optional (default: (-inf, inf)): Lower and upper joint angle limit
joint_typestr, optional (default: ‘revolute’): Joint type: revolute, prismatic, or fixed (continuous is the same as revolute)

set_joint(joint_name, value)[source]#

Set joint position.

Note that joint values are clipped to their limits.

Parameters:

joint_namestr: Name of the joint
valuefloat: Joint angle in radians in case of revolute joints or position in case of prismatic joint.

Raises:

KeyError: If joint_name is unknown

get_joint_limits(joint_name)[source]#

Get limits of a joint.

Parameters:

joint_namestr: Name of the joint

Returns:

limitspair of float: Lower and upper joint angle limit

Raises:

KeyError: If joint_name is unknown

load_urdf(urdf_xml, mesh_path=None, package_dir=None)[source]#

Load URDF file into transformation manager.

Parameters:

urdf_xmlstr: Robot definition in URDF
mesh_pathstr, optional (default: None): Path in which we search for meshes that are defined in the URDF. Meshes will be ignored if it is set to None and no ‘package_dir’ is given.
package_dirstr, optional (default: None): Some URDFs start file names with ‘package://’ to refer to the ROS package in which these files (textures, meshes) are located. This variable defines to which path this prefix will be resolved.

plot_visuals(frame, ax=None, ax_s=1, wireframe=False, convex_hull_of_mesh=True, alpha=0.3)[source]#

Plot all visuals in a given reference frame.

Visuals can be boxes, spheres, cylinders, or meshes. Note that visuals that cannot be connected to the reference frame are omitted.

Parameters:

frameHashable: Reference frame
axMatplotlib 3d axis, optional (default: None): If the axis is None, a new 3d axis will be created
ax_sfloat, optional (default: 1): Scaling of the new matplotlib 3d axis
wireframebool, optional (default: False): Plot wireframe (surface otherwise)
convex_hull_of_meshbool, optional (default: True): Displays convex hull of meshes instead of the original mesh. This makes plotting a lot faster with complex meshes.
alphafloat, optional (default: 0.3): Alpha value of the surface / wireframe that will be plotted

Returns:

axMatplotlib 3d axis: New or old axis

plot_collision_objects(frame, ax=None, ax_s=1, wireframe=True, convex_hull_of_mesh=True, alpha=1.0)[source]#

Plot all collision objects in a given reference frame.

Collision objects can be boxes, spheres, cylinders, or meshes. Note that collision objects that cannot be connected to the reference frame are omitted.

Parameters:

frameHashable: Reference frame
axMatplotlib 3d axis, optional (default: None): If the axis is None, a new 3d axis will be created
ax_sfloat, optional (default: 1): Scaling of the new matplotlib 3d axis
wireframebool, optional (default: True): Plot wireframe (surface otherwise)
convex_hull_of_meshbool, optional (default: True): Displays convex hull of meshes instead of the original mesh. This makes plotting a lot faster with complex meshes.
alphafloat, optional (default: 1): Alpha value of the surface / wireframe that will be plotted

Returns:

axMatplotlib 3d axis: New or old axis

add_transform(from_frame, to_frame, A2B)#

Parameters:

from_frameHashable: Name of the frame for which the transformation is added in the to_frame coordinate system
to_frameHashable: Name of the frame in which the transformation is defined
A2BAny: Transformation from ‘from_frame’ to ‘to_frame’

Returns:

selfTransformManager: This object for chaining

check_consistency()#

Check consistency of the known transformations.

The complexity of this is between $O(n^2)$ and $O(n^3)$, where $n$ is the number of nodes. In graphs where each pair of nodes is directly connected the complexity is $O(n^2)$. In graphs that are actually paths, the complexity is $O(n^3)$.

Returns:

consistentbool: Is the graph consistent, i.e. is A2B always the same as the inverse of B2A?

connected_components()#

Get number of connected components.

If the number is larger than 1 there will be frames without connections.

Returns:

n_connected_componentsint: Number of connected components.

static from_dict(tm_dict)#

Create transform manager from dict.

Parameters:

tm_dictdict: Serializable dict.

Returns:

tmTransformManager: Deserialized transform manager.

get_transform(from_frame, to_frame)#

Request a transformation.

Parameters:

from_frameHashable: Name of the frame for which the transformation is requested in the to_frame coordinate system
to_frameHashable: Name of the frame in which the transformation is defined

Returns:

A2BAny: Transformation from ‘from_frame’ to ‘to_frame’

Raises:

KeyError: If one of the frames is unknown or there is no connection between them

has_frame(frame)#

Check if frame has been registered.

Parameters:

frameHashable: Frame name

Returns:

has_framebool: Frame is registered

plot_connections_in(frame, ax=None, ax_s=1, whitelist=None, **kwargs)#

Plot direct frame connections in a given reference frame.

A line between each pair of frames for which a direct transformation is known will be plotted. Direct means that either A2B or B2A has been added to the transformation manager.

Note that frames that cannot be connected to the reference frame are omitted.

Parameters:

frameHashable: Reference frame
axMatplotlib 3d axis, optional (default: None): If the axis is None, a new 3d axis will be created
ax_sfloat, optional (default: 1): Scaling of the new matplotlib 3d axis
whitelistlist, optional (default: None): Both frames of a connection must be in the whitelist to plot the connection
kwargsdict, optional (default: {}): Additional arguments for the plotting functions, e.g. alpha

Returns:

axMatplotlib 3d axis: New or old axis

Raises:

KeyError: If the frame is unknown

plot_frames_in(frame, ax=None, s=1.0, ax_s=1, show_name=True, whitelist=None, **kwargs)#

Plot all frames in a given reference frame.

Note that frames that cannot be connected to the reference frame are omitted.

Parameters:

frameHashable: Reference frame
axMatplotlib 3d axis, optional (default: None): If the axis is None, a new 3d axis will be created
sfloat, optional (default: 1): Scaling of the frame that will be drawn
ax_sfloat, optional (default: 1): Scaling of the new matplotlib 3d axis
show_namebool, optional (default: True): Print node names
whitelistlist, optional (default: None): Frames that must be plotted
kwargsdict, optional (default: {}): Additional arguments for the plotting functions, e.g. alpha

Returns:

axMatplotlib 3d axis: New or old axis

Raises:

KeyError: If the frame is unknown

remove_frame(frame)#

Remove a frame (node) from the graph.

Parameters:

frameHashable: The frame to remove.

Returns:

selfTransformManager: This object for chaining.

remove_transform(from_frame, to_frame)#

Remove a transformation.

Nothing happens if there is no such transformation.

Parameters:

from_frameHashable: Name of the frame for which the transformation is added in the to_frame coordinate system
to_frameHashable: Name of the frame in which the transformation is defined

Returns:

selfTransformManager: This object for chaining

set_transform_manager_state(tm_dict)#

Set state of transform manager from dict.

Parameters:

tm_dictdict: Serializable dict.

to_dict()#

Convert the transform manager to a dict that is serializable.

Returns:

tm_dictdict: Serializable dict.

property transforms#: Rigid transformations between nodes.

write_png(filename, prog=None)#

Create PNG from dot graph of the transformations.

Warning

Note that this method requires the Python package pydot and an existing installation of graphviz on your system.

Parameters:

filenamestr: Name of the output file. Should end with ‘.png’.
progstr, optional (default: dot): Name of GraphViz executable that can be found in the $PATH or absolute path to GraphViz executable. Possible options are, for example, ‘dot’, ‘twopi’, ‘neato’, ‘circo’, ‘fdp’, ‘sfdp’.

Raises: