Building a 6 DOF Model

The techniques learned here will be consistent with all Visual3D models. However the model described in this tutorial is only designed to illustrate the principles of model building and should not be considered the Default Visual3D lower-body model. Once the User learns the basics of building models it is up to him or her to decide what model and marker set is most appropriate for their analyses.

This tutorial follows the YouTube 6DoF Model Building tutorial. The YouTube video can be found here.

There are 6 basic steps to performing an analysis of motion capture data in Visual3D:

Create a model of your subject using a standing trial and define the linked segments
Explore your movement trials, and associate them with your model
Perform any signal and event processing required
Define any biomechanical model-based calculations (joint angles, moments, powers, etc.)
Generate the desired reports
If desired, export data for statistical processing

In this tutorial we will:

Load a standing calibration trial
Define various segments to create a lower-body a gait model.

Key Concepts

A calibration file (often referred to as a Standing Trial or a Static Trial) is a short motion capture of the subject in a stationary pose. Marker positions are averaged automatically over all frames to compensate for noise in the data. NOTE: If the subject moved during the standing trial, you can specify a subset of frames using the Modify Frame Range For Static Calibration command from the Model Menu items.

Anatomical markers or Calibration markers are placed at anatomically relevant locations (e.g. palpable bony landmarks near segment endpoints).
Tracking markers are placed at convenient locations for tracking the segments. Suggested rules for marker placement on rigid clusters is described in the following article:
Cappozzo A, Cappello A, Della Croce U, Pensalfini P (1997) Surface-Marker Cluster Design Criteria for 3-D Bone Movement Reconstruction. IEEE Transactions on Biomedical Engineering, 44 (12), p 1165-1174.

Preparing for the Tutorial

1. Ensure that version 3.0 or later of Visual3D has been downloaded and installed.
2. Download the sample data.
3. Save this file in the folder where you plan to save your motion capture files.
NOTE: The download contains the end result of this tutorial. It may be useful as a secondary resource for verifying your progress.
4. Launch the Visual3D program from the Start menu.
The program will open to the main workspace.

Before completing this tutorial please review the 3D Viewer Animation Controls.

Create a Hybrid Model

1. From the Model menu, select Create -> Hybrid Model from C3D file.

2. A dialog titled Select the calibration file for the new model will appear;

Select Sub01_StandingStaticCal01.c3d Click Open.

3. Visual3D will switch to Model Building mode automatically. The 3D viewer will display the average value of the marker locations from the standing file. The dialog bar to the left of the screen will contain a list of segments, which by default will contain only a segment representing the Laboratory (e.g. Motion Capture Volume).
Note: Your screen may look slightly different.

3D View Options

Throughout this tutorial, play with some of the 3D view options to familiarize yourself with these options:

With your mouse, use the 3D Viewer Animation Controls. to rotate/pan your view of the model.

1. Click the View Target ID toggle button on the toolbar until the target names appear.

2. Click the View Segment toggle button on the toolbar until the pelvis bone disappears (the same effect can be achieved by pressing F5 on your keyboard).

3. Click the View Segment Geometry toggle button on the toolbar until you toggle off geometric view the pelvis (the same effect can be achieved by pressing F7 on your keyboard).

4. Click the View Segment Lines toggle button on the toolbar until you toggle off the yellow lines which connect the segment end points.

Creating the Pelvis Segment

There are many possible markers for a pelvis segment that make sense anatomically, and have a history in the biomechanics community. Visual3D offers 3 default pelvis segments:

1) Visual3D Pelvis - The default pelvis segment in Visual3D is labeled a Visual3D Pelvis since the pelvis can be constructed as any other segment. Visual3D inherited this definition from MOVE3D (the precursor software to Visual3D) and has been used by the staff in the Physical Disabilities Branch at the NIH for more than 20 years.

2) CODA Pelvis - The CODA pelvis defines the location of the Hip Joint Centers using regression equations from the Bell and Brand articles.

3) Helen Hayes (Davis) Pelvis - The Helen Hayes (Davis) pelvis defines the location of the Hip Joint Centers using regression equations from the Davis article.

In this tutorial we are presenting the CODA pelvis:

1. On the segments tab:

1. From the Segment Name box, select Pelvis.

2. From the Segment Type box, select Coda.

3. Click Create.

2. In the Coda Segment Markers dialog box, enter these values:

1. Define Calibration targets:

(Right/Left Anterior and Posterior Iliac Crest Markers)

R.ASIS RIAS

L.ASIS LIAS

R.PSIS RIPS

L.PSIS LIPS

2. Check Use Calibration Targets for Tracking

3. Close Coda Segment Markers dialog box

3. Click Build Model to build the segment. You should now see a pelvis segment on your standing model. If you do not see the pelvis segment after clicking Build Model, double check the values you entered in the last step.

View the Pelvis Segment Coordinate System

It is often helpful to isolate the segment's coordinate system in order to validate that it is setup correctly. This view can also help you visualize where the center of gravity for a segment is located. Follow the procedure below to isolate the segment's coordinate system by toggling off the other views. When you are done you will be left with the Coordinate System of the Pelvis as represented by a Red Line (x-axis), Green Line (y-axis) and a Blue Line (z-axis).

Note: Each of the view buttons is a toggle button and will either toggle on or off a particular view.

Click the Views Segment toggle button on the toolbar until the pelvis bone disappears (the same effect can be achieved by pressing F5 on your keyboard).
Click the Views Segment Geometry toggle button on the toolbar until you toggle off geometric view the pelvis (the same effect can be achieved by pressing F7 on your keyboard).
Note: If you have followed this tutorial exactly this view may already be off.
Click the Views Segment Lines toggle button on the toolbar until you toggle off the yellow lines which connect the segment end points.

Segment Properties

At this point, the Segment Properties for the Pelvis can be modified if you would like. More information about Segment Properties, can be found here.

A little fun with the Graphics

You may skip to this section if you wish. It is possible to replace the ”bones” with another bone or object file. As a ridiculous example, you can change the pelvis model to display a skull rather than the pelvis bones. This example can be found here.

Save the data

Save often to prevent loss of files due to power outages or Windows errors.

Save the Workspace to a .cmz file

Maintain a series of .cmz files as you work so that you can revert to a previous step.

From the File menu, click on Save As.
In the Save As dialog box label your file MyTutorial1.cmz, navigate to the location of your choice and click Save.

Save the Model Template

Save the segment definitions as a model template (mdh) file to allow you to re-create models using the same marker set.

From the Model menu select Save Model Template.

In the Save As dialog box label your file Tutorial_ModelTemplate.mdh, navigate to the location of your choice and click Save.

Apply the Model Template

Now that the model template exists, you can use this template on other data sets.

From the Model menu select Apply Model Template

In the dialog box select the appropriate .mdh file.

Define the Remaining Segments

Create the Right Thigh Segment

1. Create Thigh Segment:

From the Segments tab, select Right Thigh in the Segment Name drop down list box
Click Create. A new tab labeled Right Thigh will open.
In the Right Thigh tab, enter these values:

Define Proximal Joint and Radius Lateral: None Joint: RIGHT_HIP Medial: None Radius: 0.5DISTANCE(RIGHT_HIP,LEFT_HIP)* Define Distal Joint and Radius Lateral: RFLE Joint: None Medial: RFME Select Tracking Targets: RTH1, RTH2, RTH3, RTH4

Click Build Model. A 3D image of a thigh will appear.
Note: If you receive an error message about inertial properties and custom segments, you may have entered an incorrect number for the proximal radius.
Click Close Tab before proceeding.
Note: Closing the tab will not affect the model in any way.

Create the Right Shank Segment

1. Create Virtual Knee Joint Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: RIGHT_KNEE

   Landmark Name: RIGHT_KNEE

   Define Orientation Using:
   Starting Point: RFLE
   Ending Point: RFME
Offset Using the Following AXIAL Offset: 0.5
Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

2. Create Shank Segment:

In the Segments tab, select Right Shank in the Segment Name box.
Click on the Create Segment button.

In the Right Shank tab, enter these values:

Define Proximal Joint and Radius Lateral: None Joint: RIGHT_KNEE Medial: None Radius: RTH_DISTAL_RADIUS Define Distal Joint and Radius Lateral: RFAL Joint: None Medial: RTAM Select Tracking Targets: RSHK1, RSHK2, RSHK3, RSHK4

Click on Build Model. A 3D image of a shank will appear distal to the thigh.
Click on Close Tab before proceeding.

Create Right Foot Segment

1. Create Virtual Knee Ankle Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: RIGHT_ANKLE

   Landmark Name: RIGHT_ANKLE

   Define Orientation Using:
   Starting Point: RFAL
   Ending Point: RTAM
Offset Using the Following AXIAL Offset: 0.5
Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

2. Create Virtual Toe Ankle Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: RTOE_FT

   Landmark Name: RTOE_FT

   Define Orientation Using:
   Starting Point: RFCC
   Ending Point: R5MH
   Lateral Object: R1MH
   Project From: RTOE
Do NOT Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

3. Create Foot Segment:

In the Segments tab, select Right Foot in the Segment Name box.
Click on the Create Segment button.

In the Right Foot tab, enter these values:

Define Proximal Joint and Radius Lateral: None Joint: RIGHT_ANKLE Medial: None Radius: RSK_DISTAL_RADIUS Define Distal Joint and Radius Lateral: None Joint: RTOE_FT Medial: None Radius: 0.5DISTANCE(R1MH,R5MH)* Extra Target to Define Orientation Location: Lateral R5MH Select Tracking Targets: R1MH, R5MH, RFCC, RTOE

Click on Build Model. A 3D image of a foot will appear distal to the shank.
Click on Close Tab before proceeding.

Create the Left Thigh Segment

1. Create Thigh Segment:

In the Segments tab, select Left Thigh in the Segment Name box.
Click on the Create Segment button.

To Automatically Populate Left Thigh Information:

Click Guess Properties button NOTE:The segment information should auto populate. Make sure to check all values. The segment definitions are based off the information entered for the right thigh.

OR Manually Enter Left Thigh Information:

In the Left Thigh tab, enter these values:

   Define Proximal Joint and Radius
   Lateral: None     Joint: LEFT_HIP     Medial: None
   Radius: 0.5*DISTANCE(RIGHT_HIP,LEFT_HIP)

Define Distal Joint and Radius
Lateral: LFLE Joint: None Medial: LFME

Select Tracking Targets:
LTH1, LTH2, LTH3, LTH4

Click on Build Model. A 3D image of a thigh will appear.
Click on Close Tab before proceeding.

Create Landmarks for Left Segments

1. Create Virtual Knee Joint Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: LEFT_KNEE

   Landmark Name: LEFT_KNEE

   Define Orientation Using:
   Starting Point: LFLE
   Ending Point: LFME
Offset Using the Following AXIAL Offset: 0.5
Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

2. Create Virtual Knee Ankle Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: LEFT_ANKLE

   Landmark Name: LEFT_ANKLE

   Define Orientation Using:
   Starting Point: LFAL
   Ending Point: LTAM
Offset Using the Following AXIAL Offset: 0.5
Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

3. Create Virtual Toe Ankle Center:

Click Landmarks button
Click Add New Landmark button
Create Landmark: LTOE_FT

   Landmark Name: LTOE_FT

   Define Orientation Using:
   Starting Point: LFCC
   Ending Point: L5MH
   Lateral Object: L1MH
   Project From: LTOE
Do NOT Check: Offset by Percent (1.0 = 100%)
Check: Calibration Only Landmark

Create the Left Shank Segment

1. Create Shank Segment:

In the Segments tab, select Left Shank in the Segment Name box.
Click on the Create Segment button.

To Automatically Populate Left Shank Information:

Click Guess Properties button NOTE:The segment information should auto populate. Make sure to check all values. The segment definitions are based off the information entered for the right thigh.

OR Manually Enter Left Shank Information:

In the Left Shank tab, enter these values: Define Proximal Joint and Radius Lateral: None Joint: LEFT_KNEE Medial: None Radius: LTH_DISTAL_RADIUS Define Distal Joint and Radius Lateral: LFAL Joint: None Medial: LTAM Select Tracking Targets: LSHK1, LSHK2, LSHK3, LSHK4

Click on Build Model. A 3D image of a shank will appear distal to the thigh.
Click on Close Tab before proceeding.

Create the Left Foot Segment

1. Create Foot Segment:

In the Segments tab, select Left Foot in the Segment Name box.
Click on the Create Segment button.