URDF

URDF parsing and importing

URDF parsing is done via the class method from_urdf_file of the Chain class.

There are multiple things to consider to parse a URDF file :

URDF and IKPy conventions

An URDF robot is made of links and joints : each joint represents a motor, and is bound to two links : his parent link and his child link.

Be careful, the links of IKPy (and of the matlab toolbox) are more related to the URDF joints!

On the picture below, here we have a robot arm in the URDF style :

In the URDF style, the robot generally begins and ends with a "URDF Link", which don't exist in our IKPy representation.

That's why IKPy automatically adds two links (this time IKPy Links), at the beginning and the end of our robot :

Giving the base elements

If your robot is not a linear chain (for example a humanoid), you must extract your chain in your URDF file. To achieve this, the import function uses the parameter base_elements.

Using a last_link_vector

Specifying a chain mask

In IKPy, you can activate or deactivate at will some links

For example, in a 4 links Chain, by specifying the mask :

[True, True, False, True]

You will activate every link, but the third one :

To use the link, mask, use the parameter active_links_mask when creating the Chain object.