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FusionHub BASE combines data from an outside-in tracking system with inertial measurements via an IMU.

Setup

  • Setup your optical tracking system. Attach the IMU to the optical target or attach both to the same rigid object eg. an HMD. Initialize the optical tracking body in your motion capture software and note the object ID.

  • Connect your IMU to the computer running FusionHub. Make sure your computer can connect to the IMU and read data by using LpmsControl 2. Make sure to disconnect from LpmsControl before running FusionHub.

  • Modify config.json to contain the correct information for your IMU and optical tracking system. See below how to configure the various block of the configuration file. The configuration file can also be modified through the FusionHub GUI as shown further below.

Calibration

There are two calibration steps that are required to operate the BASE filter:

Gyroscope Autocalibration

Gyroscope sensors have a built-in measurement bias that changes over time and is temperature-dependent. Good temperature calibration of MEMS gyroscopes is usually not possibkle, therefore FusionHub offers teh possibility to run-time calibrate this offset. This calibration is semi-automatic.

The measurement bias of the gyroscope attached to the tracked object is calculated as an average of data acquired over a certain interval. Requirement for this sampling to happen is for the object to be in a non-moving / static state. The state of the object is determined by the input from the optical tracking. So once the optical tracking system (eg. ART DTrack) reports the optical target to be static, gyroscope data will be sampled, averaged and a new bias compensation value calculated.

The result of the autocalibration is saved in autoCalVal.json. When starting FusionHub for the first time, this offset is set to (0, 0, 0). Make sure to place the target with the IMU attached within the tracking volume and keep it static eg. by placing it on the floor.

IMU-Optical Intercalibration

The IMU-optical intercalibration calibrates the orientation difference between IMU and the optical tracking body. When setting up a new system or after modifying the optical target a (re-)calibration is needed. The calibration is started by running FusionHub with the runIntercalibration option set to true.

Rotate the target with the IMU attached slowly within the tracking volume. You can monitor the status of the intercalibration in the Intercalibration section on the Fusion Config page of the GUI. After around 50 sampled poses the intercalibration should be finished and the GUI should show the resulting calibration quaternion.

Click Apply Intercalibration Result to automatically insert the result in the configuration file. Click Set and Save at the bottom of the editor to save the result and restart FusionHub.

Check the 3D View page to confirm if the intercalibration result is correct. The red and white cube mostly overlap when you rotate your object inside the tracking volume. Note that after a restart it might take a few seconds for optical and fused pose to converge.

IMU-Optical Fusion Filter

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