3.53 WorldInfo
WorldInfo { |
The WorldInfo node provides general information on the simulated world:
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The title field should briefly describe the purpose of the world.
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The info field should give additional information, like the author who created the world, the date of creation and a description of the purpose of the world. Several character strings can be used.
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The gravity field defines the gravitational acceleration to be used in physics simulation. The gravity is set by default to the gravity found on earth. You should change it if you want to simulate rover robots on Mars, for example. The gravity vector defines the orientation of the ground plane used by InertialUnits.
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The CFM and ERP fields correspond to the physics simulation world parameters used by ODE. See the ODE documentation for more details of these parameters.
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The fast2d field allows the user to switch to Fast2d mode. If the fast2d field is not empty, Webots tries to load a Fast2d plugin with the given name. Subsequent kinematics, collision detection, and sensor measurements are computed using the plugin. The objective is to carry out these calculations using a simple 2D world model that can be computed faster than the 3D equivalent. The Webots distribution comes with a pre-programmed plugin called "enki." In addition, a Webots user can implement his own plugin. However, Fast2d mode is limited to simple world models containing only cylindrical and rectangular shapes. The Webots distribution contains an example of world using Fast2d: khepera_fast2d.wbt (located in the projects/robots/khepera/worlds directory of Webots). For more information on the Fast2d plugin, please refer to chapter 7.
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The physics field refers to a physics plugin which allows the user to program custom physics effects using the ODE API. See chapter 6 for a description on how to set up a physics plugin. This is especially useful for modeling hydrodynamic forces, wind, non-uniform friction, etc.
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The sound is an experimental field not effective yet.
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The basicTimeStep field defines the duration of the simulation step executed by Webots. It is a floating point value expressed in milliseconds. The minimum value for this parameter is 0.001, that is, one microsecond. Setting this field to a high value will accelerate the simulation, but will decrease the accuracy and the stability, especially for physics computations and collision detection. It is usually recommended to tune this value in order to find a suitable speed/accuracy trade-off.
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The displayRefresh field is multiplied by the basicTimeStep value to define how frequently the 3D display of the main window is refreshed in normal Run mode.
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The physicsDisableTime determines the amount of simulation time (in seconds) before the idle solids are automatically disabled from the physics computation. Set this to zero to disable solids as soon as they become idle. This field matchs directly with the dBodySetAutoDisableTime ODE function. This feature can improve significantly the speed of the simulation if the solids are static most of the time. The solids are enabled again after any interaction (collision, movement, ...).
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The physicsDisableLinearThreshold determines the solid's linear velocity threshold (in meter/seconds) for automatic disabling. The body's linear velocity magnitude must be less than this threshold for it to be considered idle. This field is only useful if physicsDisableTime is bigger or equal to zero. This field matchs directly with the dBodySetAutoDisableLinearThreshold ODE function.
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The physicsDisableAngularThreshold determines the solid's angular velocity threshold (in radian/seconds) for automatic disabling. The body's angular velocity magnitude must be less than this threshold for it to be considered idle. This field is only useful if physicsDisableTime is bigger or equal to zero. This field matchs directly with the dBodySetAutoDisableAngularThreshold ODE function.
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The defaultDamping field allows to specifiy a Damping node that defines the default damping parameters that must be applied to each Solid in the simulation.
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If the inkEvaporation field is set to a non-null value, the colors of the ground textures will slowly turn to white. This is useful on a white-textured ground in conjunction with a Pen device, in order to have the track drawn by the Pen device disappear progressively. The inkEvaporation field should be a positive floating point value defining the speed of evaporation. This evaporation process is a computationally expensive task, hence the ground textures are updated only every WorldInfo.basicTimeStep * WorldInfo.displayRefresh milliseconds (even in fast mode). Also, it is recommended to use ground textures with low resolution to speed up this process. As with the pen device, the modified ground textures can be seen only through infra-red distance sensors, and not through cameras (as the ground textures are not updated on the controller side).
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The northDirection field is used to indicate the direction of the virtual north and is used by Compass and InertialUnit nodes.
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The lineScale field allows the user to control the size of the optionally rendered arbitrary-sized lines or objects such as the connector and the servo axes, the local coordinate systems and centers of mass of solid nodes, the rays of light sensors, the point light representations, the camera frustums, or the offsets used for drawing bounding objects. The value of this field is somehow arbitrary, but setting this value equal to the average size of a robot (expressed in meter) is likely to be a good initial choice.
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The contactProperties field allows to specifiy a number of ContactProperties nodes that define the behavior when Solid nodes collide.