Bridge Plugins

Bridge plugins are custom bridge implementations that can be used by an ego vehicle to send and receive sensor data. Bridge plugins must be built by the simulator and the resulting bundle named bridge_XXX must be placed in the AssetBundles/Bridges folder. If running the binary, this folder is included in the downloaded .zip file. If running in Unity Editor (Developer Mode), the sensor will be built into the folder directly. This must be done before running the simulator (running the executable or pressing Play in the Editor).

Building bridge plugins to a bundle is done as below:

  1. Open Simulator -> Build... menu item
  2. Select bridge plugins in Bridges section of build window
  3. Build plugins with Build button

To make a bridge plugin, create a folder in Assets/External/Bridges, for example Assets/External/Bridge/CustomBridge.

Inside this folder you must place all the scripts that will be used by the simulator to build C# managed assembly.

Implementation top#

A bridge plugin must provide two separate classes inheriting the following interfaces:

1) IBridgeFactory

2) IBridgeInstance

Factory class is used to provide meta-information about bridge and a few factory methods. It will be created only once.

Instance class represents the actual bridge implementation that is able to send and/or receive data. It will be created once for every vehicle where it is used.

Bridge Factory top#

    public interface IBridgeFactory
    {
        IBridgeInstance CreateInstance();
        void Register(IBridgePlugin plugin);
        void RegPublisher<DataType, BridgeType>(IBridgePlugin plugin, Func<DataType, BridgeType> converter);
        void RegSubscriber<DataType, BridgeType>(IBridgePlugin plugin, Func<BridgeType, DataType> converter);
    }

This interface requires the class to expose four public methods:

1) CreateInstance - called to create new bridge instance. Typically this method simply returns new object of class that implements IBridgeInstance interface.

2) Register - called by simulator allow factory register supported functionality with plugin interface. See the section below on plugin registration.

3) RegPublisher and RegSubscriber - called by custom sensors to register custom data types for publisher or subscriber functionality. Factory can use this method itself to register its supported data types for simulator built-in sensors.

Classes inheriting from this interface must have BridgeNameand BridgeType attribute applied to inform name and type that will be used to identify this bridge. For example:

    [BridgeName("MyCustomBridge", "MyCustomBridgeType")]
    public class MyCustomBridgeFactory : IBridgeFactory
    {
        ...
    }

Bridge Instance top#

    public interface IBridgeInstance
    {
        Status Status { get; }
        void Connect(string connection);
        void Disconnect();
    }

This interface requires the class to expose three public methods:

1) Status - getter that will be called by simulator to query status of bridge. For example, sensors will be sending data only if Status is set to Connected state.

1) Connect - called when simulator wants to initate new connection. Connection string is passed unmodified from web interface where it can be set to anything. It is responsibility of bridge implementation to validate then accept or reject this string.

2) Disconnect - called when simulator wants to close connection. Typically called upon unloading vehicle from scene.

Bridge Plugin Registration top#

Upon creating a bridge factory, the simulator will call Register method to allow factory and pass plugin instance that factory should use to register available data types and publishers/subscribers. This information is not static as custom sensor plugins may want to register their custom types with one or multiple bridge factories.

Simulator provides many different data types, for example ImageData or PointCloudData that represents specific instances of data published or subscribed by sensors. Factory must inform plugin about which types it supports. This is performed by calling AddType<DataType>(string bridgeTypeName) on plugin instance. DataType is one of the data types simulator supports. bridgeTypeName is an arbitrary string used to show name of this data type in UI.

For each subscriber or publisher bridge factory should call AddSubscriberCreator<DataType> or AddPublisherCreator<DataType> on plugin instance. These methods should provide delegate that can be used to create subscriber or publisher instances for each sensor that wants to use specific data type.

void AddSubscriberCreator<DataType>(SubscriberCreator<DataType> subscriber);
void AddPublisherCreator<DataType>(PublisherCreator<DataType> publisher);

See IBridgePlugin.cs source code for more information on delegate arguments and return values.

Typically, the bridge will call AddType + AddSubscriberCreator from RegSubscriber method, and AddType + AddPublisherCreator from RegPublisher method. This should be done for all default simulator data types simulator supports.

Additionally, custom sensor plugins may choose to call your bridge RegPublisher and RegSubscriber methods to add custom data types they which to publish or subscribe. Please refer to ComfortSensor and LaneFollowingSensor sensor plugins for examples of this functionality.

Registering Plugin with Web UI top#

All bridge plugins must be registered with the SVL Simulator Web UI to be usable. This currently needs to be done manually by contacting us.

Examples top#

Open-source examples are available:

ROS Bridge - ROS bridge implementation for Autoware

ROSApollo Bridge - ROS bridge implementation for Apollo

ROS2 Bridge - ROS2 bridge implementation

CyberRT Bridge - CyberRT bridge implementation

Logging Bridge - simple bridge that logs all published data to a .txt file.