World

World

The world element encapsulates an entire world description including: models, scene, physics, joints, and plugins.

# Import the element creator
from pcg_gazebo.parsers.sdf import create_sdf_element

# The default world contains only the definition of the acceleration of gravity 
# and the default configuration of the physics engine using `ode`
world = create_sdf_element('world')
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="ode">
    <max_contacts>20</max_contacts>
    <max_step_size>0.001</max_step_size>
    <real_time_factor>1</real_time_factor>
    <real_time_update_rate>1000</real_time_update_rate>
  </physics>
  <gravity>0 0 -9.8</gravity>
</world>

# The physics engine can be edited using its object setter
world.physics.reset(mode='ode', with_optional_elements=True)
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="ode">
    <ode>
      <constraints>
        <cfm>0</cfm>
        <erp>0.2</erp>
        <contact_surface_layer>0.001</contact_surface_layer>
        <contact_max_correcting_vel>100</contact_max_correcting_vel>
      </constraints>
      <solver>
        <type>quick</type>
        <sor>1.3</sor>
        <use_dynamic_moi_scaling>0</use_dynamic_moi_scaling>
        <friction_model>pyramid_model</friction_model>
        <min_step_size>0.0001</min_step_size>
        <precon_iters>0</precon_iters>
        <iters>50</iters>
      </solver>
    </ode>
    <max_contacts>20</max_contacts>
    <max_step_size>0.001</max_step_size>
    <real_time_factor>1</real_time_factor>
    <real_time_update_rate>1000</real_time_update_rate>
  </physics>
  <gravity>0 0 -9.8</gravity>
</world>

world.physics.reset(mode='bullet', with_optional_elements=True)
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="bullet">
    <max_contacts>20</max_contacts>
    <max_step_size>0.001</max_step_size>
    <bullet>
      <constraints>
        <cfm>0</cfm>
        <split_impulse>1</split_impulse>
        <split_impulse_penetration_threshold>-0.01</split_impulse_penetration_threshold>
        <contact_surface_layer>0.001</contact_surface_layer>
        <erp>0.2</erp>
      </constraints>
      <solver>
        <type>quick</type>
        <sor>1.3</sor>
        <iters>50</iters>
        <min_step_size>0.0001</min_step_size>
      </solver>
    </bullet>
    <real_time_update_rate>1000</real_time_update_rate>
    <real_time_factor>1</real_time_factor>
  </physics>
  <gravity>0 0 -9.8</gravity>
</world>

world.physics.reset(mode='simbody', with_optional_elements=True)
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="simbody">
    <max_contacts>20</max_contacts>
    <simbody>
      <accuracy>0.001</accuracy>
      <min_step_size>0.0001</min_step_size>
      <contact>
        <plastic_impact_velocity>0.5</plastic_impact_velocity>
        <plastic_coef_restitution>0.5</plastic_coef_restitution>
        <stiffness>100000000.0</stiffness>
        <dissipation>100</dissipation>
        <override_stiction_transition_velocity>0.001</override_stiction_transition_velocity>
        <viscous_friction>0</viscous_friction>
        <dynamic_friction>0.9</dynamic_friction>
        <static_friction>0.9</static_friction>
        <override_impact_capture_velocity>0.001</override_impact_capture_velocity>
      </contact>
      <max_transient_velocity>0.01</max_transient_velocity>
    </simbody>
    <max_step_size>0.001</max_step_size>
    <real_time_factor>1</real_time_factor>
    <real_time_update_rate>1000</real_time_update_rate>
  </physics>
  <gravity>0 0 -9.8</gravity>
</world>

# A world can contain multiple models, add an empty model by using the add_model method
world.reset()
world.add_model('model_1')
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="ode">
    <max_contacts>20</max_contacts>
    <max_step_size>0.001</max_step_size>
    <real_time_factor>1</real_time_factor>
    <real_time_update_rate>1000</real_time_update_rate>
  </physics>
  <gravity>0 0 -9.8</gravity>
  <model name="model_1"/>
</world>

# You can add a model to the world as well
model = create_sdf_element('model')
world.add_model('model_2', model)
print(world)

<world name="default">
  <physics default="1" name="default_physics" type="ode">
    <max_contacts>20</max_contacts>
    <max_step_size>0.001</max_step_size>
    <real_time_factor>1</real_time_factor>
    <real_time_update_rate>1000</real_time_update_rate>
  </physics>
  <gravity>0 0 -9.8</gravity>
  <model name="model_1"/>
  <model name="model_2"/>
</world>

# You must have unique names for the models in a world
world.add_model('model_1')

Model element with name model_1 already exists