Changing Role of Geometries

Question

I'm trying to remove the proximity role from certain geometries. However, I'm getting an error that my plant source id is not registered:

Referenced geometry source 0 is not registered.

I have checked that the plant is indeed registered, since calling

plant->RegisterAsSourceForSceneGraph(scene_graph);

fails with !geometry_source_is_registered().

I've also created geometries (by adding a sdf model), so source_id should be valid. Here's how I'm attempting this:

drake::systems::DiagramBuilder<double> builder;
drake::multibody::MultibodyPlant<double>* plant{};
drake::geometry::SceneGraph<double>* scene_graph{};
std::tie(plant, scene_graph) = drake::multibody::AddMultibodyPlantSceneGraph(&builder, timestep);

drake::multibody::Parser parser(plant, scene_graph);

const auto robot_model_index = parser.AddModelFromFile(sdf_filepath, "robot");

plant->Finalize();
const auto& source_id = plant->get_source_id().value();

const auto& inspector = scene_graph->model_inspector();

auto all_geom_ids = inspector.GetAllGeometryIds();
for (auto& geom_id : all_geom_ids) {
    const auto frame_id = inspector.GetFrameId(geom_id);
    const auto geom_model_index = inspector.GetFrameGroup(frame_id);
    // https://stackoverflow.com/questions/68225198/does-a-modelinstance-in-a-multibodyplan-have-a-unique-source-id-for-determining
    if (geom_model_index == robot_model_index) {

        // This fails: Referenced geometry source 0 is not registered.
        scene_graph->RemoveRole(source_id, geom_id, drake::geometry::Role::kProximity);
    }
}

Answer 1

If you want to change geometry associated with the a MultibodyPlant, the source_id to use is the plant.get_source_id().