NOTE: It's recommended to use the updated version of this tutorial found here!!!!
There are 6 basic steps to performing an analysis of motion capture data in Visual3D:
In this tutorial we will load a standing calibration trial and define various segments to create a lower-body a gait 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.
During this tutorial, you will learn how to:
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, a subset of frames, in which the subject is stationary, can be selected for computing the average locations of the markers. The command Modify Frame Range For Static Calibration is located in the Model Menu items.
In this figure, Anatomical 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.
NOTE: The file Tutorial1.cmo contains the end results of this tutorial.
It may be useful as a secondary resource for verifying your progress.
The program will open to the main workspace.
The viewer is a 3D display (using the OpenGL libraries) of your marker set as seen from multiple camera angles.
The left mouse button is used to modify the orientation of the 3D model. Holding down the left mouse button and moving the mouse up and down rotates the model up and down, moving the mouse from side to side rotates the model from side to side.
The right mouse button is used to modify the scaling of the model. Holding down the right mouse button and moving the mouse up or right moves the camera closer to the center of the model (increases the size of the image displayed). Holding down the right mouse button and moving the mouse down or left moves the camera further from the center of the model (decreases the size of the image displayed).
Holding down the center mouse button (or both the left and right mouse buttons together on a 2-button mouse), allows the user to shift (translate) the model from side to side and up or down.
Note: You will notice that once you move the model a white cross-hair is temporarily added to the scene. This is provided to assist you with centering your model in the scene.
Sets the camera's perspective to view the front of the model from the anterior direction as defined by the lab's anterior/posterior axis.
Sets the camera's perspective to view the side of the model from the alter direction as defined by the lab's medial/lateral axis.
Allows you to view the model from any angle. This is the default view when the 3D Viewer is first opened. This view allows you to choose the camera's perspective by dragging the mouse around the scene.
Sets the camera to look at the lab origin. If you have gotten “lost” in the scene, you can use this button to quickly get you back to a “known” point, the lab's origin.
Cycles through target labels, target labels with landmark labels, or no target labels.
Clicking the View Segments toggle button will toggle on and off the model files assigned to the segments. The model files are wire frame objects formatted as either a .v3g or .obj file or a VRML .wrl file. The model file is usually a representation of the bone(s) used for the 3D animation. In the example the model file is a 3D representation of the pelvis bone.
Note: The 3D animation object is purely for visualization. You can rotate, scale or move the bones relative to the segment coordinate system and it will not affect the analysis.
To view the geometry click the View Segment Geometry toggle button on the toolbar.
View segment lines allows you to view a “stick figure” of the segment(s).
click the View Segment Lines toggle button.
The yellow segment lines displayed are:
A vertical line between the segment endpoints
Two horizontal lines between the medial and lateral radii of the segment (e.g. from the segment endpoint to the medial and lateral borders of the segment, which are one radius away.)
Start → Programs → C-Motion → Visual3D Create a new model using the standing trial
select ”Lower Body Static Trial.c3d.” Click Open.
Note: Your screen may look slightly different.
There are many possible markers for a pelvis segment that make sense anatomically, and have a history in the biomechanics community. The most common marker set is the Helen Hayes marker set shown here.
In this tutorial we are presenting a pelvis segment that is defined similarly to all segments in Visual3D, so we refer to it as the Visual3D Pelvis
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) in the image below.
Note: Each of the view buttons is a toggle button and will either toggle on or off a particular view.
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.
The following properties are computed based on the calibration of the segment proximal and distal endpoints.
The Segment Properties dialog modifies general properties which are common to most segments. Some of the most common uses include changing the mass of the segment, the scale and rotation of the object which represents the segment, adding a custom object (such as a golf club or baseball bat), removing the kinetic calculations for a segment, modifying the size and rotation of the segment, and modifying the segment coordinate system.
You may skip to the next section if you wish. As you will see, 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.
Note: For older versions of the software this will be head.obj. Visual 3D accepts either file format.
Save often to prevent loss of files due to power outages or Windows errors.
Maintain a series of .cmo files as you work so that you can revert to a previous step.
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_template.mdh, navigate to the location of your choice and click Save.
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.
Note: If you receive an error message about inertial properties and custom segments, you may have entered an incorrect number for the proximal radius.
Note: Closing the tab will not affect the model in any way.
Define Proximal Joint and Radius
Lateral: RLK Joint: none Medial: RMK Radius:
Define Distal Joint and Radius
Lateral: RLA Joint: none Medial: RMA Radius:
Select Tracking Targets: RSK1, RSK2, RSK3, RSK4
Define Proximal Joint and Radius
Lateral: RLA Joint: none Medial: RMA Radius:
Define Distal Joint and Radius
Lateral: RFT1 Joint: none Medial: none Radius: 0.06
Select Tracking Targets: RFT1, RFT2, RFT3
Note: The value of 0.06 was a measurement made on this subject. This value should be measured and should be unique to each subject.
Define Proximal Joint and Radius
Lateral: LHP Joint: none Medial: none Radius: 0.089
Define Distal Joint and Radius
Lateral: LLK Joint: none Medial: LMK Radius:
Select Tracking Targets: LTH1, LTH2, LTH3, LTH4
Define Proximal Joint and Radius
Lateral: LLK Joint: none Medial: LMK Radius:
Define Distal Joint and Radius
Lateral: LLA Joint: none Medial: LMA Radius:
Select Tracking Targets: LSK1, LSK2, LSK3, LSK4
Define Proximal Joint and Radius
Lateral: LLA Joint: none Medial: LMA Radius:
Define Distal Joint and Radius
Lateral: LFT1 Joint: none Medial: none Radius: 0.06
Select Tracking Targets: LFT1, LFT2, LFT3
Proceed to next Tutorial: Visualizing Data