Webots: Spawn multiple nodes and disable collision between them, but not the environment

Question

In Webots, I am spawning 10 vehicle nodes at the same time and position for reinforcement learning. I would like the vehicles to not interact with each other (collision and LIDAR) but still have physics to collide with the environment.

So my question:

Is there provision in Webots for disabling collision and LIDAR point cloud between certain nodes (so that they can pass through each other), but retain physics to interact with the environment?

Answer 1

Yes, it is possible to disable collision and LIDAR detection with a specific node in Webots.

These are two different tasks that can be achieved with the following solutions.

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Disable collision

To control the collision detection you have to write a physics plugin. At this link you can find all the information about how to set it up.

The main point is to overwrite the webots_physics_collide(dGeomID g1, dGeomID g2) callback function, and if both the geometries g1 and g2 belong to a vehicle node then you just have to return 1 to tell the physics engine to ignore the collision.

The biggest development effort in your physics plugin will be to detect if an ODE geometry belongs to a vehicle. In a physics plugin you can use all the ODE API functions (ODE is the Webots' physics engine). In particular you might be interested in these funtions to get the ODE body from a dGeomId, check if two bodies are connected by a joint, and get a ODE body/geom given a Webots DEF name.

// ODE functions
dBodyID dGeomGetBody (dGeomID)
int dAreConnected (dBodyID, dBodyID);
// Webots utility functions
dBodyID dWebotsGetBodyFromDEF(const char *DEF);
dGeomID dWebotsGetGeomFromDEF(const char *DEF);

Here you can find an example of pyhsics plugin just to have an idea about how to structure it. However, note that the functionality implemented in the webots_physics_collide(dGeomID g1, dGeomID g2) differs from what you would like to achieve.

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Disable LIDAR detetion

You can use the Supervisor function wb_supervisor_node_set_visibility.

So, in the controller where you are spawning the vehicles you would have to add something like this (just pseudo code)

foreach (string vehicle_name, vehicles) {
  WbNodeRef vehicle_node = wb_supervisor_node_get_def(vehicle_name);
  foreach (string other_vehicle_name, vehicles) {
    if (vehicle_name == other_vehicle_name)
      continue;
    // assuming expects the vehicle has a unique DEF name and
    // the LIDAR is visible in the Webots scene tree with DEF name 'LIDAR'
    WbNodeRef lidar_node = wb_supervisor_node_get_def(vehicle_name + '.LIDAR'); 
    wb_supervisor_node_set_visibility(vehicle_node, lidar_node);
}

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Disclaimer: I am a Webots developer working at Cyberbotics.