Tutorial RT Biofeedback - Vicon Nexus

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Overview

This tutorial shows is step-by-step guide to stream real-time data from a Nexus (Vicon) to Visual3D to take advantage of the real-time data processing and biofeedback* capabilities.

Nexus streams out the data it receives as it processes them. Visual3D can save the streamed frames out to a C3D file, or directly capture a static trial from the data streaming in.

Capturing data in Visual3D is desirable for capturing a static trial in preparation for real-time digitizing or functional joints. Our real-time biofeedback (part of Visual3D Professional) will also support capturing data on an event trigger, which is also a unique way of capturing the last 'n' seconds of data when an event happens which you can't predict ahead of time to start a manual capture. You would probably want to use Nexus to capture other times in order to prevent loss of data or to customize the parameter section of the C3D file being captured.

  • RT Biofeedback is available only in Visual3D Professional.

Step 1 - Subject Calibration in Nexus

Before streaming in real time, Nexus must be running and the subject calibration trial must be labeled. This allows Nexus to label markers in "Live" mode.

1. Calibrating the capture volume Nexus using the software's standard protocol.

2. Create a subject either using a predefined template in Nexus or creating your own. (image on right)

Nexus Subject.png

3. Collect a static trial.

4. From data managent, load the static trial and label the marker trajectories.(image on right)

Nexus Marker Labelling.png

5. Run the 'Calculate Autolabel Trial Parameters' from the Pipeline menu (image on right). This allows Nexus to label markers in "Live" mode.

Nexus AutoLabel.png

6. Go back to "Live" mode, with the subject in the capture volume to test that Nexus correctly autolabels markers in real-time.

7. Before launching real-time streaming in Visual3D, take note of the system file currently selected. (image on right)

Nexus System.png

Step 2 - Apply Model Template in Visual3D

To create the segments in Visual3D, you must first load a static trial into Visual3D and apply a model template (.mdh).

To load the static trial, you can either:
OPTION 1 - Load the static trial you collected in Nexus during Step 1
OPTION 2 - You can collect a static trial in Visual3D.

I recommend using the static trial collected in Nexus (Option 1).

OPTION 1 -

1. Go to the Models tab of Visual3D
2. Go to Model -> Create (Add Static Calibration File) -> Hybrid Model from C3DFile and browse to the C3D file which was collected in Nexus.
3. Go to Model -> Apply Model Template and browse to your model template (.mdh)


OPTION 2 -

Collect a short static trial using the following process:

1. From the Model menu, select Create (Add Static Calibration File), then Hybrid Model from RealTime Streaming.

Create Model RT.png

2. Define the name of the model:

Model Name RT.png

3. Select the correct real-time system from the drop down menu and click start streaming.

When prompted, specify your sampling frequency
When prompted, specify the IP address as the local host, 127.0.0.1 and port as 801

4. While the subject is standing still, collect a static trial by either clicking Create Snapshot (Static Trial) to save the static trial in the workspace or Save Static File to Disk to save the static trial as a C3D file.

Please note that closing the Real Time Model Building dialog box will stop the real time streaming and remove the markers from the 3D viewer. After closing this dialog, if the static trial does not appear in the 3D viewer, switch to the Workspace tab and back to the Models tab.

Model Snapshot RT.png

4. Go to Model -> Apply Model Template and browse to your model template (.mdh)

Step 3 - Visual3D Real-Time Set Up

1. Launch V3D (V3D main screen)

V3D main screen.jpg

2. Select the Real-time capture TAB

3. a) In the dialog box you should see your plug in ______.dlls Click Vicon_DataStream_RT


Vicon DataStream RT.png


3. b) A dialog box will appear to select your current Nexus System file. When using standard Nexus file structure, the system file should be located under: C:\ProgramData\Vicon\Nexus\Configurations\Systems

Nexus System Select.png

4. Then set the point rate to Nexus' sampling frequency.

Point Rate Select.png

5. Identify the local host as 127.0.0.1 and port as 801.

The local host on a computer is always 127.0.0.1. If you are streaming between two different computers, you would need to specify a different IP.

IP Server Settings.png

Streaming data from Nexus is continuous. Note: streaming status in lower left

It is very important that Nexus automatic labelling works properly in "Live" mode and identifies markers correctly. If the markers aren't correctly identified in Nexus, Visual3D can not process any realtime data.

After streaming for a long period of time, the labeling in Nexus may start to fail. In Nexus, clicking CTRL+R may improve the labeling.

Step 4 - Compute model based item: RT pipeline

The RT Pipeline is available only in Visual3D Professional

After having created or loaded a model, and established connection with the system back in the Real-Time tab, it is then possible to compute any model based item through the real-time pipeline.

  1. Open up Model Based Data Computation under the Real-Time Pipeline
  2. Double click Compute_Model_Based_Data
  3. Click Edit
    RTPipeline CMBD.jpg
  4. Change the corresponding:
    Data Name: Ankle
    Folder: ORIGINAL
    Model Based Item Properties: JOINT_ANGLE
    Segment: Right Foot
    Reference Segment: Right Shank
    Capture Model Based Data.jpg
  5. Click Done

Step 5 - Create Graph

  1. Click Add in the Real-Time Graphs section, and enter the following:
    Data to: LINK_MODEL_BASED::ORIGINAL::Ankle
    GraphDef.jpg
  2. Click OK


Your result should show a Real-Time stream that looks like the picture below

Final Graph RT.png

Remember to save the Graph and RT Pipeline

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