def parse_schema(schema_path):
"""Parses the schema XML.
Args:
schema_path: Path to the schema XML file.
Returns:
An `ElementSpec` for the root element in the schema.
"""
with resources.GetResourceAsFile(schema_path) as file_handle:
schema_xml = etree.parse(file_handle).getroot()
return _parse_element(schema_xml)
def _make_model(n_bodies,
n_actuators,
random,
stiffness_range=(15, 25),
damping_range=(0, 0)):
"""Returns an MJCF XML string defining a model of springs and dampers.
Args:
n_bodies: An integer, the number of bodies (DoFs) in the system.
n_actuators: An integer, the number of actuated bodies.
random: A `numpy.random.RandomState` instance.
stiffness_range: A tuple containing minimum and maximum stiffness. Each
joint's stiffness is sampled uniformly from this interval.
damping_range: A tuple containing minimum and maximum damping. Each joint's
damping is sampled uniformly from this interval.
Returns:
An MJCF string describing the linear system.
Raises:
ValueError: If the number of bodies or actuators is erronous.
"""
if n_bodies < 1 or n_actuators < 1:
raise ValueError('At least 1 body and 1 actuator required.')
if n_actuators > n_bodies:
raise ValueError('At most 1 actuator per body.')
file_path = os.path.join(os.path.dirname(__file__), 'lqr.xml')
with resources.GetResourceAsFile(file_path) as xml_file:
mjcf = xml_tools.parse(xml_file)
parent = mjcf.find('./worldbody')
actuator = etree.SubElement(mjcf.getroot(), 'actuator')
tendon = etree.SubElement(mjcf.getroot(), 'tendon')
for body in range(n_bodies):
# Inserting body.
child = _make_body(body, stiffness_range, damping_range, random)
site_name = 'site_{}'.format(body)
child.append(etree.Element('site', name=site_name))
if body == 0:
child.set('pos', '.25 0 .1')
# Add actuators to the first n_actuators bodies.
if body < n_actuators:
# Adding actuator.
joint_name = 'joint_{}'.format(body)
motor_name = 'motor_{}'.format(body)
child.find('joint').set('name', joint_name)
actuator.append(
etree.Element('motor', name=motor_name, joint=joint_name))
# Add a tendon between consecutive bodies (for visualisation purposes only).
if body < n_bodies - 1:
child_site_name = 'site_{}'.format(body + 1)
tendon_name = 'tendon_{}'.format(body)
spatial = etree.SubElement(tendon, 'spatial', name=tendon_name)
spatial.append(etree.Element('site', site=site_name))
spatial.append(etree.Element('site', site=child_site_name))
parent.append(child)
parent = child
return etree.tostring(mjcf, pretty_print=True)