Visual3D and Theia

Working with Theia3D Data in Visual3D

Theia3D exports motion capture results in C3D format, which can be opened directly in Visual3D for additional analysis and post-processing. This allows users to combine Theia’s markerless motion capture with the modeling, processing, and visualization tools available in Visual3D.

After processing trials in Theia3D, the resulting kinematic data can be exported and imported into Visual3D without the need for markers or manual labeling. When exporting data, Theia generates two versions of the output:

File	Description
pose_0.c3d	Unfiltered kinematic data
pose_filt_0.c3d	Filtered kinematic data using the smoothing frequency selected during processing

The filtered file is typically recommended for most biomechanical analyses, as it reduces high-frequency noise in the reconstructed motion.

Theia .c3d files integrate directly into Visual3D through an automatic model template. This removes the need to manually define a biomechanical model from static trial landmarks, simplifying and speeding up the analysis workflow. The same model template is applied to all individuals’ .c3d files. However, the resulting model remains subject-specific, as segment lengths and scaling parameters are derived from the model generated by Theia3D and stored in the .c3d file.

Note that the Mass and Height values shown in the Subject Data / Metrics tab in Visual3D are default Visual3D values and are not imported from Theia.

Automatic Signals

When the automatic Visual3D model is applied, several useful signals are created automatically. These signals mainly fall into two categories: LANDMARK and KINETIC_KINEMATIC.

LANDMARK signals include two anatomical points: L_HEEL and R_HEEL. These heel landmarks are commonly used for gait event detection, such as identifying heel-strike events.

The model also generates multiple KINETIC_KINEMATIC signals for each body segment. These signals are organized into folders for each segments. The segment default names can be found here.

These automatically generated signals provide a useful starting point for analyzing biomechanical data from Theia .c3d files. For all other processing tasks usually undertaken in Visual3D such as event generation, link-model-based calculations, and signal exporting, these can be easily accomplished using Visual3D’s powerful and flexible Pipeline Workshop.

For more detailed information please visit our Working with Theia3D Data in Visual3D Blog Post

Post-Processing Theia3D Data for New Visual3D Users

A very brief summary of some of Visual3D’s capabilities include:

• Automated data processing using pipeline commands

• Use pipeline parameters to store variable strings for use in combination with pipeline commands

• Efficient organization of related .c3d files using workspaces, including tags to group trials

• Flexible event creation, to identify specific moments within a movement

• Wide-ranging model-based calculations, metric calculations, and mathematical expressions

• Quick exporting functionality

A few steps when post processing in Visual3D will include:

Open Files

• Open the .c3d files in Visual3D.

Assign Tags

• Assign the appropriate tags to the files.

Create Events

• Create the events required for the movement being analyzed.

Compute Signals

• Compute the relevant biomechanical signals.

Compute Metrics

• Calculate the metrics based on the computed signals.

Save Workspace

• Save the workspace to preserve the processed pipeline.

Export Signals and Metrics

• Export_Data_To_ASCII_File or the Export_Data_To_Matfile pipeline commands can be used to providing the signals or metrics you wish to export

For a more detailed version please visit our Post-Processing Theia3D Data for New Visual3D Users Blog post

Integrating External Devices With Theia3D Kinematics

When it comes to integrating external devices with markerless kinematics, only camera systems that support synchronization of external devices can be used to integrate such signals (e.g. Qualisys Miqus, Vicon Vue/FLIR Blackfly S). It’s also important to note that Theia3D itself does not handle the .c3d files from external devices - all integration of these signals with markerless kinematics is performed as a post-processing step in Visual3D.

Signals from external devices such as force plates, instrumented treadmills, or EMG systems can be integrated with Theia3D markerless kinematics during post-processing in Visual3D using the Manage_Theia3D_Merge / Manage_File_Merge command or through the Import_Signals_From_C3D_File pipeline command. More information regarding this can be found in our blog post Integrating External Devices With Theia3D Kinematics