Introduction

FusionHub is a software application that has the purpose of combining various sensor data inputs to create a higher level data output. There are 3 basic versions of FusionHub:

• FusionHub BASE combines data from an outside-in tracking system with inertial measurements via an IMU. Typical applications: Head-mounted display tracking for VR/AR applications, camera tracking for virtual production

• FusionHub MOVE adds an additional platform IMU to the BASE configuration. It combines data from both IMUs to calculate poses relative to a moving platform. Typical applications: AR/VR in a vehicle, aircraft, or on a simulator platform

• FusionHub FLOW combines odometry, GPS and IMU data from a vehicle to calculate high-accuracy and low-latency global localization information. Typical applications: Automobile localization, robot localization

The diagram below shows the general structure of FusionHub. Sources and sinks are connected by a filter unit. The sensor fusion functionality is contained in this filter unit. The filter parameters as well as the parameters of input and output blocks can be configured via a configuration script or the graphical user interface.

The graphical user interface is detached from the main FusionHub application and both applications can therefore run on separate computers. This provides flexibility for running FusionHub on devices with limited monitoring capabilities like a head mounted display.

General

Running FusionHub

FusionHub consists of two components:

• The main application

• A graphical user interface application

The main FusionHub application is started by running FusionHub.exe. No specific installation is needed, the application can be run directly out of its deployment directory. It is a command line application that uses the file config.json for its configuration. We will explan the contents and options of the configuration file further below.

Please install the graphical user interface by running lp-fusionhub-dashboard_0.1.0_x64_en-US.msi. It installs lp-fusionhub-dashboard in your start menu, launch the application from there. Press the Connect button after starting FusionHub.exe to connect client and server. In case you are running FusionHub on a separate machine make sure to enter the correct IP address.

Communication with External Applications

Sending FusionHub Data to External Applications via the ZeroMQ Interface

FusionHub emits data resulting from the sensor fusion through the local network interface.

Output Ports

The network port that this information is output to can be configured in the JSON parameter file config.json of FusionHub.

Data Format

As low level protocol to emit the output data we use ZeroMQ (publisher / subscriber). The data itself is in JSON format and is encoded as Protocol Buffers. Protocol Buffers are documented here. Message are defined in the Protobuf (.protoc) format as defined in the file stream_data.proto. This file is contained in the installation folder of FusionHub.

Python Resources

Download a Python example that shows how to decode messaged from FusionHub from this repository.

Prerequisites can be installed in your Python 3 environment with this:

pip install zmq
pip install protobuf

Make sure to set the input port in FusionHubPythonExample.py correctly. For example for the Antilatency source definition like below, the port needs to be set to 8899.

"optical": {
    "type": "Antilatency",
    "settings": {
        // Use this for access from an external process eg. ALVR
        "endpoint": "tcp://*:8899",
        
        "environmentLink": "AntilatencyAltEnvironmentHorizontalGrid~AgAEBLhTiT_cRqA-r45jvZqZmT4AAAAAAAAAAACamRk_AQQCAwICAgICAQICAAI",
        "placementLink": "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
    }
}

C# Resources

On parsing Protobuf files: https://github.com/5argon/protobuf-unity

How to subscribe to ZeroMQ messages: https://github.com/gench23/unity-zeromq-client and https://tech.uqido.com/2020/09/29/zeromq-in-unity/

VRPN Output

VRPN output is set in the following part in the sinks section of config.json. The device name will be referenced by the plugin for Unreal engine.

"VRPN": {
  "settings": {
    "deviceName": "Fusion Hub"
  }
}	  

Please see below how we achieve data input via VRPN in the Unreal engine. First, install the VRPN LiveLink plugin:

Configure the VRPN source with the correct device and subject name:

Apply the output from the fusion hub to an Unreal object eg. a cine camera actor.

FLOW Filter Configuration

The FLOW filter has two operation modes with different configuration blocks in config.json and different output formats. The two modes are:

• Low-dynamics filter (LD)

• High-dynamics filter (HD)

Low-dynamics Filter (Odometry + GPS + (some) IMU)

Configuration block example (in sinks section)

"gnssImuFusion": {
    "echoFusedPose": false,
    "endpoint": "tcp://*:8803",
    "fuser": {
        "fitModel": "ModelGnssImu",
        "accelError": 0.01,
        "omegaError": 0.02,
        "measurementError": 0.05,
        "imuToCarRotation": {
            "w": 1,
            "x": 0,
            "y": -1,
            "z": 0
        }
    }
}

Output data format

{
  "fusedVehiclePose": {
    "acceleration": {
      "x": -0.4263402493894084,
      "y": -0.14872631710022688,
      "z": 9.790632347106932
    },
    "globalPosition": {
      "x": 1.8985360999771979,
      "y": 41.50585830111033
    },
    "lastDataTime": {
      "timestamp": 0
    },
    "position": {
      "x": 0,
      "y": 0
    },
    "timestamp": {
      "timestamp": 48347424440200
    },
    "utmZone": "31T",
    "yaw": 0
  }
}

High-Dynamics Filter (IMU + GPS)

Configuration block example (in sinks section)

// Sensor fusion config
"vehicularFusion": {
    "echoFusedPose": false,
    "endpoint": "tcp://*:8801",
    "fuser": {
        "fitModel": "SimpleCarModel",
        "driveModel": "Differential",
        "velError": 0.277777778,
        "omegaError": 0.5,
        "measurementError": 0.1,
        "smoothFit": true
    }
}

Output data format

{
    "fusedVehiclePose": {
        "acceleration": {
            "x": 0.0,
            "y": 0.0,
            "z": 0.0
        },
        "globalPosition": {
            "x": 1.8982356601544925,
            "y": 41.50544434418204
        },
        "lastDataTime": {
            "timestamp": 0
        },
        "position": {
            "x": -25.38332083641826,
            "y": -36.403733501197635
        },
        "timestamp": {
            "timestamp": 48910226723400
        },
        "utmZone": "31T",
        "yaw": 0.1555754684457767
    }
}

{
	"fusedPose": {
		"lastDataTime": {
			"timestamp": 0
		},
		"orientation": {
			"w": 0.4437907292666558,
			"x": 0.5659687502206026,
			"y": -0.4749652416904733,
			"z": 0.5070869566224411
		},
		"position": {
			"x": -25.383320836418306,
			"y": -36.403733501197166,
			"z": 163.98272320756405
		},
		"timestamp": {
			"timestamp": 48910226723400
		}
	}
}