Visual3D™
Analysis and Reporting Tutorial
(3.0 Edition)
C-Motion, Inc.
15821-A Crabbs Branch Way
Rockville, MD 20855 USA
(301) 840-1919 (phone)
(301) 840-0271 (fax)
support@c-motion.com
Table of Contents
How to Use the Visual3D
™
Tutorials...............................................................................................1
Visual3D Tutorial # 4 ................................................................................................................2
The Visual3D Workspace...........................................................................................................3
Starting Visual3D...............................................................................................................4
Load the Motion and Model File .............................................................................................4
File Tags .............................................................................................................................5
Model Based Calculations .......................................................................................................6
Analysis Goal.....................................................................................................................6
Creating a Report .................................................................................................................7
Creating Joint Angles........................................................................................................... 10
Adding to the Report ........................................................................................................... 14
Report Page Layout .......................................................................................................... 18
Recalculating ..................................................................................................................... 19
Other Link Model Based Data Calculations ............................................................................... 20
Segment Angles............................................................................................................... 20
Joint Centers ................................................................................................................... 20
Joint Angles .................................................................................................................... 20
Joint Forces .................................................................................................................... 21
Joint Moments................................................................................................................. 21
Joint Power ..................................................................................................................... 22
Link Model Calculations........................................................................................................ 23
Acknowledgements: The development of Visual3D software was funded in part by STTR grant (R43 HD3728601) from the National Institute of Child Health and Human Development (NICHD). C-Motion also gratefully
acknowledges and appreciates the assistance provided by the Rehabilitation Medicine Department in the Warren
Grant Magnuson Clinical Center at the National Institutes of Health.
ii
How to Use the Visual3D™ Tutorials
Welcome to C-Motion’s Visual3D motion analysis software. This is
the last of four tutorials. The Visual3D software provides the
kinematics and kinetic (inverse dynamics) calculations needed for
biomechanical analysis, as will be seen in this tutorial.
After motion capture data has been collected, there are several
steps to performing a motion analysis in which Visual3D is needed.
You need to:
1. Create a model of the subject(s) using a subject standing
calibration file, and define the linked segments
2. Validate the movement data and associate the movement
data with the model
3. Perform any desired signal and event processing
4. Define any biomechanical model based calculations for
angles, moments, powers, and other metrics.
5. Generate the desired kinematic and kinetic analysis reports
For this reason, there are four (4) tutorials available. They cover:
1. Modeling
2. Data and Force Plate Validation
3. Signal, Event, and Pipeline Processing
4. Analysis and Reporting
Each tutorial picks up where the last one ended, but the results of
each tutorial are saved as a .cmo file so that you may skip a part
that you already are familiar with, or try out different features and
capabilities during a tutorial - using it only as a guideline.
The tutorial instructions are
given in this column.
Screen shots and explanations are provided in this column, and the
tutorial instructions are listed in the right column.
Various sample input files will be needed, and can be downloaded
from the web site at:
http://www.c-motion.com/support/tutorials.htm
We hope you find Visual3D useful. We are constantly improving the
product, and if you have any suggestions for enhancements or new
features, we would love to hear them. Just drop us a note at
info@c-motion.com any time.
May, 2004
1
Visual3D Tutorial # 4
It is assumed that Visual3D has been installed and a model has
been created as described in the first tutorial. Likewise, we assume
that a movement trial has been assigned to a model and the data
processed and validated – from the third tutorial.
We will be doing a lower body gait analysis in a collection of
tutorials. The techniques and processes followed are easily
transferred to sports, neuroscience, animation, or other applications
since we are focusing on the tool, not the analysis.
To start the tutorial, we need to pick up where the third one ended
– with a completed model and assigned motio n file saved as a .cmo
file. This can also be downloaded.
You may optionally try to enhance the script file from the third
tutorial. These need to be downloaded. These files can be found
on the web site in the Example at:
Use the .cmo file from the
third tutorial or download it.
It is called:
“Signal Processing.cmo”
The following script file is
optional: “Model and Process
Sample.v3s”
http://www.c-motion.com/support/tutorials.htm
This tutorial is focused on, signal and event processing, and using
the Pipeline processor in Visual3D.
The file “Report Processing.cmo ” contains the end results of this
tutorial and may be used to check your progress and/or as input for
the subsequent analysis and reporting tutorials.
May, 2004
Save the files in a location on
your computer where you
would normally save motion
capture files.
2
The Visual3D Workspace
Visual3D creates a unique Workspace into which capture data is
added, models are integrated, and reports are produced. The whole
workspace can then be saved and shared as a digital report in
which all the underlying analysis, data, and models can be
referenced.
The entire Visual3D Workspace is contained in a special file, with
the extension “.cmo ” (for C-Motion Output).
In this tutorial we will process a movement trial. The file itself is
never touched. Instead, it is copied into the workspace. Even in
the workspace, the original data is not modified, but is maintained
so that all calculations and signal processing results can be
recreated.
As a clinical and research tool, Visual3D keeps track of the
processing done to data so that unwarranted assumptions are not
made, and consistent outcomes are reached every time the same
data is used. This is also why we prefer getting raw data from
systems rather than processed data (i.e. no interpolating, filtering,
or pre-processing). For example, if all we have is ground reaction
data from a force plate as input, we have to assume that all the
force plate properties, calibrations, and processing was perfect
since there is no way to validate the data. This leads to
unwarranted assumptions and possible invalid analytical results.
Visual3D is designed to work
with raw data as a way to
avoid making unwarranted
assumptions and generating
valid, reproducible results.
The above information is in each tutorial, but this tutorial is the one
where actual analysis concepts and reporting capabilities are simply
touched on. The idea here is to become familiar with the tool, so
that you know where to look when you want to try something new.
May, 2004
3
Starting Visual3D
Launch the program from you Windows Start menu. After a brief
title screen display, the program opens with an empty Visual3D
Workspace. The Visual3D Workspace tab displays the contents of
the current workspace – which can be saved as a .cmo file.
Start Visual3D:
Start ->
Programs - >
C-Motion ->
Visual3D
Load the Motion and Model File
First we will open the data saved earlier as a .cmo file. We will add
the movement trial to the workspace.
From the File menu, select
Open - >
Signal Processing.cmo
The next step is to develop the analysis plan. Since this is simply a
tutorial, we will be creating a gait analysis report of only a few
specific measures. The other tutorials took a step by step approach
in order to explain basic features. In this tutorial we will be taking
a more interactive approach. We will create some kinetic and
kinematic calculations using out basic link- model (i.e. a model of
segments linked together). But first, there is a powerful feature
that is used in customizing your analysis called Tags…
May, 2004
4
File Tags
File tags are used to differentiate or group movement trials. In this
way calculations can be performed against a select set of movement
trials, and reports can be created based on a subset of movement
data.
Movement trials can have multiple tags assigned. For example, all
files associated with trials in which the subjects walked barefoot can
have a tag labeled "Bare Foot" assigned to them. Those trials that
are "Bare Foot" and are only women subjects could have another
tag labeled "Female" to that file. A graph in the report can then
display only files with a certain tag.
Tags are most easily created on the Workspace Status Tab in
visual3D by clicking the “Add New File Tag” button. Fine-tuning
tags on thousands of motion trails can be done using the
File- >”Add/Modify File Tags” option.
Switch to the Workspace
Status tab
Click on the “Add New Tag”
button
Enter ‘Sample Tag” as its
name
Check the box so the new tag
is used, and not deleted
Tags are added to the Data Tree under the Parameters folder.
Since empty folders or parameters are not saved, this means that a
tag must be used as soon as it is created in order to stick around.
It also means that any tag that is not assigned (i.e. no boxes
checked in the column) effectively doesn’t exist. To delete a tag,
simply don’t assign it to anything.
Note: Tags are used to group
files together. Reports and
model based calculations can
be constrained to tagged
files.
File tags are also displayed in the combo box on the toolbar in the
Signal and Event Processing tab. This lets any checked signals and
events for groups of trials can be collectively processed.
Tags are used to limit reporting to specific trails, and for limiting
model based calculations to only certain trials.
May, 2004
5
Model Based Calculations
If you have a Ph.D. in Kinesiology or Biomechanics, or you are an
M.D. or researcher – do not skim lightly or jump completely over
these sections. This tutorial is written without as much jargon as
possible to address a very broad customer base. However, the
interfaces and techniques described are the exactly the same
approaches and techniques used for the most sophisticated
analyses.
Warning: Even if it seems
simplistic, the process and
screens used are
fundamental.
Part of the power of Visual3D is the ability to determine exactly
what and how calculations are done – and the ability to point to the
published works proving its validity. From a pure tool perspective,
the power is in additional Pipeline command parameters and
options, and the ability to add special purpose plug-ins.
With that said, let’s move on to the analysis.
Analysis Goal
Some of the analysis characteristics we will examine will be
positions of the pelvis and foot during gait, knee flexion and
extension, and knee joint moments and powers. To do this we will
define segment angles, joint angles, joint moments, and joint
powers. We will also be reporting on basic attributes such as stride
length and other fundamental gait characteristics.
First, we will create of report with basic gait information. Then, we
will calculate joint angles to measure left and right knee
flexion/extension and add to our report these measures.
We will create a report with
joint angles for knee
flexion/extension, and some
basic gait data.
May, 2004
6
Creating a Report
A blank report exists by default in the Visual3D Workspace. All we
need to do is go to the Reporting Tab and add the graphs we want.
Switch to the Reporting Tab
The left panel of the screen can be toggled between the Edit Report
Dialog and an Animation view by clicking the Edit Report toolbar
icon – the one that looks like a colorful checkerboard.
The report toolbar icon
toggles between an
animation view and the
report layout dialog box…
Add a graph to the report at
• Page 1
• Row 1
• Column 1
• Select the “Temporal and
Distance Metrics”
• Click the Add button
When a model is created in Visual3D, some of the more basic Gait
Analysis values are calculated and added to the data tree, notably
Kinematic and Kinetic values. When Gait events are created – such
as Heel Strikes and Toe Offs, Visual3D will calculate various
standard gait metrics, which can be presented in a pre-formatted
single chart. These metrics are related to gait movements over
time – thus are called “Temporal Metrics.”
On Page 1, Row 1, Column 1 – Add a Temporal and Distance
Metrics chart. Select all of the items to graph and fill in the event
names. A title for the graph can also be entered.
May, 2004
7
Give the graph the title
‘Temporal and Distance
Metrics’
Select all the Distance Items
Enter the proper event labels
Click Done
Note that by default the
graph took up the whole
page.
As you add new graphs in
rows and columns, Visual3D
will attempt to dynamically
rescale the page so that the
whole page is being used.
To see a whole page of a
report…
The following pages describe each metric.
Click the Show/Hide Edit
Dialog toolbar icon (it toggles
the animation view)
Drag the splitter bar between
panes over to the left,
eliminating the animation
window
Zoom in by clicking on the
magnifying glass icons
May, 2004
8
All metrics are constrained to the initial heel strike to the final toe
off events.
Step = (Heel Strike foot1 – Heel Strike foot2) The time from one
foot making contact until the other foot makes contact.
Step Length = Distance of a step in meters.
Speed – (also called Cadence) Walking rate of steps in meters per
second, and normalized to Statures per second. A Stature is a step
length/height, and compensates for the different height and weight
characteristics between patients.
Stride = (Heel Strike – Heel Strike) When one foot makes contact
until it makes contact again.
Stride Width and Length – Length is the distance from Heel
Strike to Heel Strike. Stride width is the distance between the
opposite Heel Strike to the stride vector (HS-HS). Both are
averaged for the number of strides found in the event range. This
number (or count) is always given in parenthesis.
May, 2004
9
Cycle = (Heel Strike – Heel Strike) When one foot contacts the
ground and ends when that foot contacts the ground again.
Cycle Time – A computed average and the actual numbers (count
of cycles in parenthesis) with deviation range.
Stance = (Heel Strike –Toe Off) While one foot is in continuous
contact with the ground.
Swing = (Toe Off – Heel Strike) While a foot is in the air.
Double Limb Support = (Heel Strike foot1 – Toe Off foot2) The
time when BOTH feet are on the ground during a gait cycle
Right Initial (and Left Terminal) Double limb Support Time –
The time from Right Heel Strike to Left Toe Off
Right Terminal (and Left Initial) Double Limb Support Time –
The time from Left Heel Strike to Right Toe Off.
The graphs quickly point out if a patient favors their left or right
side during gait.
Creating Joint Angles
Joint angles are defined as the orientation of one segment relative
to another segment. Because we are dealing with 3D space, there
are a series of rotational transformations involved in the calculation.
A joint angle is not the same as a 3-point or 4-point angle in which
there are projections, but no transformations (more on this later).
Back to the tutorial…
Visual3D lets you pick any 2 segments in which to measure a joint
angle. They do not have to be connected – or even be near each
other. In practice, joint angles are calculated as the transformation
from one segment (A) to another segment (B) using the local
coordinate system of segment B as the frame of reference.
It is essential that you select the proper Cardan sequence based on
a complete understanding of what you are trying to measure. It is
beyond the scope of this document to explain the concepts behind
the 3D order of rotations/transformations that go into calculating
joint angles.
In Visual3D, you can choose the Cardan sequence you want. The
default Cardan sequence used by Visual3D is the ordered sequence
of rotations (x, y, z) that assumes that the Z axis is in the
up/dow n/Axia l direction and the Y axis is Anterior/Posterior, or the
direction if travel. (Yeadon, 1990; Davis et al., 1991; Kadaba et
al., 1990), where:
X = flexion/extension
Y = abduction/adduction
Z = longitudinal rotation
May, 2004
This is trying to explain that
Knee Flexion/Extension is
calculated by rotating the
shank segment around the Xaxis of the thigh segment and
measuring the rotation
needed to align the Y and Z
axes – on a frame by frame
basis…
10
One of the options for joint angles is to select normalization (not
generally recommended due to a high level of uncertainty).
Normalization means that when the segments in the movement trial
are in the same relative posture as the same segments in the
standing trial, the joint angle is considered zero. The problem with
the calculation of a normalized angle (as we have done it) is that
the standing posture and the movement trial should both be aligned
with the laboratory axis. Getting a patient to stand oriented relative
to the lab may not be possible. An alternative approach is to create
Virtual Segments that define the desired angle in the standing
posture.
Normalization is not used in
this tutorial joint angle
definition – too many subtle
things can affect the results.
Experience is needed for that
one...
Let’s create joint angles for measuring the flexion/extension of the
each knee.
In Visual3D, from MODEL in the main menu bar, select Create
Model Based Data to get the following dialog box.
From the main menu bar,
select MODEL- >
Compute Model Based Data
Create a joint angle called ‘Right Knee Flexion’ (i.e. its Data Name).
The link model based property is a Joint Angle. The segment will be
The right shank and the reference segment is the right thigh.
Because we are looking for flexion/extension, which is a Euler angle
projected into the Z-Y plane, we need a transformation around the
X axis – thus the default Cardan sequence of X,Y,Z is correct. Then
press the Create button.
May, 2004
NOTE: Determining the
proper Cardan sequence
depends on the orientation of
your reference coordinate
system…
11
Data Name: Right Knee
Flexion
Properties/Calculation:
JOINT_ANGLE
Segment: Right Shank
Reference Segment (and
coordinate system): Right
Thigh
Cardan Sequence: X-Y-Z
(transform around X axis
first)
The joint angle is created and a
processing dialog shows if any
errors were encountered.
Click CREATE button
Do this again for the Left Knee.
Repeat for the Left Knee
Flexion
Click CREATE button, then
Click CLOSE
2 Joint Angles have been
created.
Switch to the Signal and
Event Processing tab…
May, 2004
12
Notice that a new folder for
LINK_MODEL_BASED items
has been created. Any
calculations relying on linked
model segments will show up
here.
This might be a good time to
save the Workspace if you
want
Notice that a new folder is created in the Data Tree for LINKMODEL-BASED calculations.
Let’s now go back to the tutorial and add a few graphs to our
report…
May, 2004
13
Adding to the Report
Switch to the Reporting tab of
the Visual3D Workspace
Reset the page number on
where to add a graph to
Page 2
Select a 2D Graph to add
Click the Add button…
The next screen is where you enter or modify data for a specific
graph.
Note: If you forgot to change
a page, row, or column you
can reset the graph’s position
here as well
Give this graph the title:
Right Knee Flexion/Extension
Make the line color Red
Notice that you can limit the
source of data by selecting
groups of movement trials in
the File/Tags to Graph combo
box…
The X-Axis should reflect
time – i.e. FRAME_NUMBERS
To see the time in seconds
(rather than from 1-100%)
select the TIME component of
the FRAME_NUMBERS, and
graph the Global Min to Max
The Y-Axis will be our Joint
Angle. Select
LINK_MODEL_BASED as the
type, and the Right Knee
Flexion calculation that we
created earlier
Click the Done button to
create the graph.
May, 2004
14
Move to PAGE 2 from the
toolbar to see the new graph
Now let’s add a graph for the
Left Knee…
Here is a time -saving trick. To pre-fill in the data for the next
graph (if it is going to be similar to another one) - highlight the
graph in the top section of the Edit Report dialog before clicking the
Add Graph button. (As shown above)
Add another 2D Graph on
page 2, row 2
Change the title to Left Knee
Flexion/Extension
Make the line Blue
Make the X-Axis show time
values
Graph the Left Knee joint
angle
NOTE: A short-cut button the
Model->Create Model Based
Data dialog is available here…
Click the Done button
May, 2004
15
Trick: Double-clicking on a
graph will zoom in on it.
Double-click again to shrink it
back…
Notice that there is a zero
baseline drawn. To remove
this, simply select the graph
by clicking on it, the rightclick and select Format
Graph…
Here you can de-select the
Show Baseline option;
change axis values; or add
grids (among other options).
The Reporting Tool in Visual3D has some additional flexibility with
graph layouts…
To consolidate the two graphs
onto a single graph, simply
change the display row in the
second graph back to 1.
May, 2004
16
A different title is needed
(highlight the graph in the
top of the left panel, click
Modify Selected button)
The graph shown to the left
removed the baseline and
displays a legend. (select,
right-click, format graph)
Reports consist of data only available in the workspace – meaning
data from the Data Tree, which c ontains the results of calculations
based on movement data, which is in turn based on a defined
model – therefore the report relies on data that only exists in the
workspace.
Report Templates can be saved (and reused), but these contain
only the definitions of the report – its graph layouts, model based
calculations, and descriptions of the data to graph – NOT the data.
A .cmo workspace file contains the report, data, and any processing
or calculations.
Save the “report template”
as:
Tutorial 4 report template.rgt
(File- >Save Report Template)
Note: This does NOT save
the DATA associated with a
report – only the formatting
any page layouts.
Note: The definitions of all
the Link Model Calculations,
like Joint Angles, are saved in
the report template as well
May, 2004
17
Report Page Layout
One of the last things to cover is page layout. First, paper size,
orientation and margins can be set by right-clicking on the report
and selecting “Options.” The second tab contains the paper layout
options.
Right-click on the report to
bring up the context menu
Select Options
Change the paper size to:
Height = 11.0
Width = 8.5
Click OK to the dialog and the
subsequent warning
message.
Note also that Visual3D automatically sizes the graphs to fit the
entire page based on the rows and columns you have created.
Page one in this tutorial has only one graph – thus one column and
row – so it takes up the whole page.
To enhance the layout or reposition a graph on the page we need to
decide on how many rows and columns will be on the page. A
graph can span columns and/or rows so that there is flexibility in
laying out each page. Because of the automatic scaling capabilities
of Visual3D, we can place a graph at the lower right hand corner of
the page first. This forces a maximum number of rows and columns
to be created, making it easier to see the layout as it happens.
TRICK: Create a small, blank bitmap file using Microsoft Paint, and
use it as the graph in the lower corner. We created the bitmap, but
put a border on it for this example so you could see how it works.
May, 2004
18
In the example below you can see that we added a bitmap at row 4,
column 4, and then rescaled the Temporal Distance graph to span 3
rows and 3 columns. You can use this trick to create lager margins
or columns anywhere you need.
Recalculating
As a final note. Since the data is not saved with a report template,
if you reload a report template, you may get graphs that simply say
“No Data” in them. You need to refresh the linkage between the
link model based calculations, the data tree, and the report. Simply
click the Recalc toolbar icon (or menu items) to refresh the
workspace calculations and the report data sources.
Click the Reclac Toolbar icon
Save your workspace!
Congratulations, you are
finished the entire set of
tutorials!
This ends the interactive part of the tutorial. Since this tutorial is
primarily focused on learning how to use the tool and knowing
where to click to get what you need, the following section is a more
detailed explanation of your analysis and reporting options.
May, 2004
19
Other Link Model Based Data Calculations
This is not part of the tutorial, but there are many other calculations
you can create and report on in addition to Joint Angles. They
include:
Note: The following 2
sections are for additional
information and not part of
the tutorial…
Segment Angles
Segment angles are defined as the orientation of one segment
relative to the laboratory. Segment angles are often calculated for
the pelvis relative to the laboratory and for the foot relative to the
laboratory. In Visual3D, there are many ways to measure segment
angles. A couple popular methods are:
1. Create a virtual segment by adding landmarks at the origin
and out along the Y axis of the lab coordinate system, and
calculating a joint angle using this new segment as the
reference segment.
2. Use either the 3-point or 4-point angle plug-ins to measure
either a Euler projected angle or a 3D angle in space.
Joint Centers
Technically, there are no joint “centers” in Visual3D (or in human
movement). A “joint” is created automatically in Visual3D when 2
segment ends are near each other. These are the yellow dots in
the model builder view. These are also the ‘joint centers’ used to
define model segments. Sometimes a ‘joint center’ is created by
hand (or identified in a calibration file). This type is different since
they are either physical markers or landmarks. The joint centers
typically referred to are usually the calculated ‘joint’ results of
adjacent segments.
Joint Angles
A joint angle requires the definition of any 2 segments. They do not
have to be connected – or even near each other. Joint angles are
defined as the orientation of one segment relative to another
segment. In practice, joint angles are calculated as the
transformation from one segment (A) to another segment (B) using
the local coordinate system of segment B as the reference as
defined by the user.
In Visual3D, you can choose the Cardan sequence you want so that
you get the results you are looking for. The default Cardan/Euler
sequence used by Visual3D is the ordered sequence of rotations (x,
y, z) (Yeadon, 1990; Davis et al., 1991; Kadaba et al., 1990),
where:
x = flexion/extension
y= abduction/adduction
z= longitudinal rotation
One of the options for joint angles is to select normalization (not
May, 2004
20
generally recommended due to a level of uncertainty).
Normalization means that when the segments in the movement trial
are in the same relative posture as the same segments in the
standing trial, the joint angle is considered zero. The problem with
the calculation of a normalized angle (as we have done it) is that
the standing posture and the movement trial should both be aligned
with the laboratory axis. Getting a patient to stand oriented relative
to the lab may not be possible. An alternative approach is to create
Virtual Segments that define the desired angle in the standing
posture.
Joint Forces
The picture below is a free body diagram of two segments, showing
the traditional assumptions for inverse dynamics (kinetic) analysis.
F1 is the “proximal segment” and F2 is the “distal segment.” The
Joint Force is the reaction force between adjacent segments.
It is assumed that:
1. The joint forces are equal and opposite about the joint
2. Joint moments are equal and opposite about the joint
3. The distal end of one segment does not need to be at the
same place as the proximal end of the other segment. This
allows movement in the joint.
Visual3D translates the force to the distal end of F1 (the proximal
segment) for the inverse dynamics calculations.
Joint Moments
Visual3D calculates the Internal Moment. If the user wants to
calculate the External Moment, another set of signals should be
calculated using the Pipeline commands under “Signal Math” to
multiply each signal by -1.
May, 2004
21
In the gait analysis literature there are three documented
approaches to describe the joint moments calculated from Inverse
Dynamics. It is important to be aware of which method is being
used so that you can tell what the sign on the moment is supposed
to be. Visual3D defaults to the first approach.
The first method presents the Net torque generated by muscles
crossing a joint (referred to as the internal moment). In the figure
above the joint moment is F2 proximal; that is the proximal
moment in the distal segment. This moment is typically resolved in
the segment coordinate system of the proximal segment (F1).
The second interpretation is based on the ground reaction force
(GRF or foot-floor constraint) being the dominant input to the body.
The extensor muscles of the legs during the stance phase of gait
counteract the GRF. This external moment is opposite in sign to the
internal moment described in the first method (e.g. –F2 proximal in
the figure).
The third interpretation is based on the sum of all extensor
moments at the ankle, knee and hip. In this interpretation all
extensor moments are assigned a positive value. One of the
consequences is that the moments at the hip and the knee (for
example) will have different sign conventions with respect to the
laboratory.
Joint Power
Joint Power is the product of the proximal joint moment and the
segment’s angular velocity.
May, 2004
22
Link Model Calculations
The Compute Model Based Data dialog box provides the ability to
define the following type of calculations…
COP_Path – Calculate the path of the Center of Pressure for a
segment with respect to some coordinate system (usually the
segment’s coordinate system). Normalization is by foot width and
length.
GRF_DATA – Calculate the Ground Reaction Force. Pick a segment
and coordinate system (usually a foot using the lab system) to use
to determine which force platform gets used. Normalization is with
the subject’s body weight.
HELICAL_ANGLE – Calculate a Segment Angle as a helix. Specify
the segment to track and in which coordinate system.
JOINT_ANGLE – Calculate the angle between 2 specified segments,
where the second one is the reference segment. Normalization is
based on matching the static trial, so coordinate systems (and A/P
direction) must match perfectly. You have the flexibility of explicitly
specifying a different Cardan sequence.
JOINT_FORCE – Calculate the forces on a joint at the distal end of a
segment. Select the joint (calculated yellow dots in the model) and
the proximal segment’s coordinate system. Normalization is with
subject mass.
JOINT_MOMENT – Calculate the moment around a joint (yellow dot
in the model). Select the joint (calculated yellow dots in the model)
and the proximal segment’s coordinate system. Normalization is
with subject mass.
JOINT_POWER – Calculate the power relative to the lab or a
segment. Select the joint (calculated yellow dots in the mo del) and
the proximal segment’s coordinate system. Normalization is with
subject mass.
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JOINT_VELOCITY – Calculate the angular velocity of the joint
between 2 segments where the second one is the reference
segment. Specify results in terms of the Lab or the reference
segment.
MODEL_COG – Tack the Center of Gravity for the whole model.
Specify the coordinate system to use – the Lab or a segment.
SEG_CGPOSITION – Calculate a segment’s Center of Gravity with
respect to another segment’s proximal end. Specify the coordinate
system to use, the lab or a segment.
SEG_DISTAL_JOINT – Calculate the joint at the distal end of a
segment relative to the proximal end of the reference segment.
Define the position relative to the segment or the lab.
SEG_PROXIMAL_JOINT– Calculate the joint at the proximal end of a
segment relative to the proximal end of the reference segment.
Define the position relative to the segment or the lab.
SEG_VELOCITY – Calculate the velocity of the center of mass of a
segment. Specify the coordinate system to use, the lab or a
segment.
TARGET_PATH – Calculate the position of a target relative to a
reference segment. Specify the coordinate system to use, the lab or
a segment.
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