1. Vicon Workstation Motion Capture Essentials
D. Gordon E. Robertson, PhD

2. Biomechanics Laboratory, School of Human Kinetics
Outline
Select appropriate marker set and type of markers
Determine number of cameras and their locations
Select appropriate location, number and types of force measuring devices (force platforms, force transducers)
Other demands: EMGs, netting, speed guns, standardized footwear and equipment?
Biomechanics Laboratory, School of Human Kinetics

3. Biomechanics Laboratory, School of Human Kinetics
1. Marker Sets
Motion capture requires selection of a suitable marker set
Types:
individual markers
clusters of markers (includes wands) on rigid structures
virtual markers (uses wands to identify body locations)
Static marker set
this set is necessary to establish joint centres and their 3D relationships with the dynamic marker set
virtual marks can be included
Dynamic marker set
this may be a reduced set that with a combination of individual markers and/or clusters
Biomechanics Laboratory, School of Human Kinetics

4. Biomechanics Laboratory, School of Human Kinetics
Static Marker Sets
subject in static posture with marker clusters
Helen Hayes marker set was a early simplified system but is not appropriate for full body 3D analyses
Vicon’s Plug-in-gait marker set is a more robust full body marker set but requires several anthropometric measurements (e.g., mass, height, leg length, knee width, ankle width, shoulder offset, elbow width, wrist width, & hand thickness)
uOttawa marker set is a modified version of Plug-in-gait. It uses hip, iliac crest, medial limb, and ear markers, but no ASIS or PSIS markers. It also requires fewer anthropometric measurements (e.g., mass, height, hip offset, & shoulder offset)
clusters may also be used for some or all segments instead of non-joint markers
Biomechanics Laboratory, School of Human Kinetics

5. Plug-in-gait Marker Set
No hip markers
No medial markers at knees, ankles, elbows, and wrists
Head markers not over ears (location of cofg)
Pelvis markers (ASIS & PSIS) are horizontally located
Only one markers on foot
Potentially arm & leg markers are linear
avoid placing markers linearly on a segment
Biomechanics Laboratory, School of Human Kinetics

6. Biomechanics Laboratory, School of Human Kinetics
uOttawa Marker Set
Hip markers
Medial markers at knees, ankles, elbows, and wrists
Head markers over ears
No ASIS or PSIS markers
Two markers for each foot, hallux optional
Potentially arm & leg markers are linear
Biomechanics Laboratory, School of Human Kinetics

7. Biomechanics Laboratory, School of Human Kinetics
Clusters
Usually 3 or 4 markers
4th marker can be offset
cluster must be well fixated to the skin
can be difficult to automatically digitize
can impede motion
Biomechanics Laboratory, School of Human Kinetics

8. Biomechanics Laboratory, School of Human Kinetics
Dynamic Marker Sets
this marker set that is similar to the static but with extraneous markers removed
medial markers
when clusters are used individual markers can be removed
Biomechanics Laboratory, School of Human Kinetics

9. Biomechanics Laboratory, School of Human Kinetics
2. Camera Setup
Number of cameras depends on complexity of task and complexity of the model
2 to 4 cameras may be sufficient for analyzing planar type motions of one side of the body
6 or more cameras for full-body models of small volumes
10 or more for large volumes such as walkways, cricket pitches
6 cameras
12 cameras
7 cameras
10 cameras, 2 overhead
Biomechanics Laboratory, School of Human Kinetics

10. Biomechanics Laboratory, School of Human Kinetics
3. Force Platforms
plates in 4 stairs and 1 in ground
two side-by-side on moveable platform
two side-by-side and one offset
Usually necessary for later kinetic analyses
One plate or multiple plates. How many?
Imbedded into floor or into stairway
Size:
small (40x60): good for starts or static jumps, easy to miss for running studies
large (60x90): good for running studies but can result in multiple feet on same plate (prevents inverse dynamics)
Location:
side-by-side, separated, alternating, movable
mounts for up to 6 large plates
Biomechanics Laboratory, School of Human Kinetics

11. Biomechanics Laboratory, School of Human Kinetics
4. Other Equipment
VO2 measurements
EMGs of leg muscles
torque resistance measured by ergometer
Biomechanics Laboratory, School of Human Kinetics

12. Example: Single Markers, Side Kick
Single markers one either side of each joint and one extra mid segment
Three force platforms
All joints can be analyzed since there are no closed loops
Biomechanics Laboratory, School of Human Kinetics

13. Example: Clusters, Olympic Lifting
Clusters identify limb segments
Two force platforms
Only ankle, knee, hip, and pelvis kinetics can be analyzed
Arms kinetics are not possible because of the bar connection
Biomechanics Laboratory, School of Human Kinetics

14. Trajectory Digitization
Vicon Workstation
Trajectory
Digitization

15. Biomechanics Laboratory, School of Human Kinetics
Steps
Calibration
Reconstruction
Labeling
Autolabeling
Defragmentation
Gap filling
Biomechanics Laboratory, School of Human Kinetics

16. Biomechanics Laboratory, School of Human Kinetics
1. Calibration
Static
origin and axes are defined
Dynamic
calibration wand is used to calibrate volume
Accuracy
usually < 1 mm
Biomechanics Laboratory, School of Human Kinetics

17. Biomechanics Laboratory, School of Human Kinetics
2. Reconstruction
Multiple 2D views to one 3D
Biomechanics Laboratory, School of Human Kinetics

18. Biomechanics Laboratory, School of Human Kinetics
3. Labeling
select the static trial
label each
trajectory
save for
autolabelling
Biomechanics Laboratory, School of Human Kinetics

19. Biomechanics Laboratory, School of Human Kinetics
4. Autolabelling
load dynamic trial(s)
apply autolabelling
Biomechanics Laboratory, School of Human Kinetics

20. Biomechanics Laboratory, School of Human Kinetics
5. Defragmentation
join line fragments with same name
Biomechanics Laboratory, School of Human Kinetics

21. Biomechanics Laboratory, School of Human Kinetics
6. Gap Filling
fill gaps with interpolating spline
Biomechanics Laboratory, School of Human Kinetics

22. Done Ready for Kinematic/Kinetic Analyses
Biomechanics Laboratory, School of Human Kinetics

23. Inverse Dynamics and Joint Power Analysis
Visual3D
Inverse Dynamics and
Joint Power Analysis

24. Biomechanics Laboratory, School of Human Kinetics
Marker and Force Data
marker data come in a .C3D file created by Vicon, Motion Analysis, Qualysis or similar motion capture system
SIMI and APAS may also be used but data must be placed in a ASCII (.FSV) file by, for example, BioProc2/3
force data come with the .C3D file but may also be collected and placed in an ASCII (.FSV) file by BioProc2/3
data may be streamed directly to Visual3D using newest version of Visual3D and compatible motion capture system, e.g., Nexus
Biomechanics Laboratory, School of Human Kinetics

25. Biomechanics Laboratory, School of Human Kinetics
Creating the Model
first a static trial is loaded to create the model (you can use a movement trial)
a previous model may be used for a similar marker set
model is customized for each participant (mass and height etc.)
ideally markers are located at each joint but these markers do not have to be included in the movement (dynamic) trials
should save the model file (.MDH) separately for use with other trials or experimental conditions of the same person
new models must be created for each new marker set
Biomechanics Laboratory, School of Human Kinetics

26. Biomechanics Laboratory, School of Human Kinetics
Model Building Screen
create segments
create landmarks
enter body mass and height
Biomechanics Laboratory, School of Human Kinetics

27. Biomechanics Laboratory, School of Human Kinetics
Movement Trials
one or more movement trials may be loaded into same workspace (.CMO), essential if trials are to be averaged
model is applied to each trial
trial may be viewed with bones or geometrical solids for each segment
ground reaction forces should be checked
errors in force platform locations and parameters may be checked and changed in necessary
Biomechanics Laboratory, School of Human Kinetics

28. Biomechanics Laboratory, School of Human Kinetics
Workspace Screen
static trials
movement trials
tags to identify experimental conditions
Biomechanics Laboratory, School of Human Kinetics

29. Biomechanics Laboratory, School of Human Kinetics
Event Labeling
if events were not created by motion capture software they can be added automatically or manually with Visual3D
special events used for reports can also be added (e.g., BEGIN, END, HIT)
events should be checked for accuracy using GUI
Biomechanics Laboratory, School of Human Kinetics

30. Signal and Event Processing Screen
event button
signal tree
body at current event
signal histories with events marked
Biomechanics Laboratory, School of Human Kinetics

31. Data Processing Pipeline
a pipeline may be applied to process the data for inverse dynamics, energy, or power analyses
a script may be used to perform these operations repeatedly
a typical script (.V3S) includes interpolation and data filtering
special forces may be added such as moving force platforms, transducer forces, or pedal forces
Biomechanics Laboratory, School of Human Kinetics

32. Biomechanics Laboratory, School of Human Kinetics
Pipeline Form
• commands • pipeline • options • import signals • opn/save scripts
Biomechanics Laboratory, School of Human Kinetics

33. Biomechanics Laboratory, School of Human Kinetics
Graphical Reports
reports, including graphs, of the various kinematics and kinetics are created next
special tags may be used to display only certain types of trials, e.g., right vs. left leg starts, barefoot vs. shod gait, loaded vs. unloaded lifts
these tags are created in the workspace area
basic reports (.RGT) may be loaded or created and saved for later repeated use
graphs may be exported for presentation
Biomechanics Laboratory, School of Human Kinetics

34. Biomechanics Laboratory, School of Human Kinetics
Reporting Screen
contents of pages
report pages
graphical or tabular reports
select page viewed here
Biomechanics Laboratory, School of Human Kinetics

35. Export Data to MatLab or BioProc3
kinematic or kinetic data may be exported in .C3D or ASCII files
BioProc3 has capability of computing total, internal and external work, angular impulses and work done by individual bursts of power
script is used to create ASCII file for BioProc3
MatLab can compute foot clearance
Biomechanics Laboratory, School of Human Kinetics

36. BioProc3: External/Internal/Total Work
external work
internal work
total work
Biomechanics Laboratory, School of Human Kinetics

37. BioProc3: Work Done in Bursts
which moment of force
peak power
peak moment
mean power
total work done
Biomechanics Laboratory, School of Human Kinetics

38. Questions? Comments? www.health.uottawa.ca/biomech/watbiom

39. Finis
Muchas Gracias