MoMo R5.1: Visualize C3D files
The fC3D toolbox is a collection of function for reading and visualisation of
C3D files. The files are imported to a Matlab struct at first. Afterwards the user
can export selected trajectories, GRFs, analog signals or parameters to arrays and
use them for individual processing. The contents of C3D files can be displayed
as 2D diagrams using the GUI ShowC3D
. 3D animations
are created by ShowC4D
, which allows a spatial navigation
as in the Vicon software and creating objects like makers, connections, planes,
arrows and tripods. The animations can be saved as picture files, AVI or
animated GIF. An ASCII-files export can be freely configured by the user.
The modification and creation of C3Ds is implemented in general, but not
recommended for standard use, because Vicon's interpretation of C3D format is
fragil. However, renaming trajectories or swapping signals of analog channels
is safe. Special formats used by Vicon to enhance the C3D standard are considered:
more than 255 trajectories, more than 65535 frames (which are just 262 seconds at
Time-critical function are implemented in C to increase the speed.
The fC3D toolbox was designed for clinical studies and diagnosis. In
consequence the reliability and stability is ver important. The different
functions have been tested ober several years in different labs under Matlab
6.5, 2008b and 2009a and with different versions of Vicon WorkStation and Nexus.
An exahustive selftest allows a quality-control on the computer system of the
The fC3D toolbox is shipped with MoMo, but it is available as standalone
ShowC3D let the user inspect the contents of one
or more C3D files in details: Signals of force plates, evaluated GRF vector
components, torsion around Z, force insertion point, EMG signals, trajectories
of markers and evaluated 3D variables, group and parameter data.
- File 1 popup-menu:
This menu allows to open several files at the same time. Select
"Add ..." to append a new so-called "tab". There are
several ways to choose a file:
1. type the file name in the edit field (no, relative or absolute path),
2. right-click in the edit field or left-click the open-folder button (open file
in folder of the current file),
3. right-click the folder button (open file in current folder, which can be
changed with momocd or
cd). C3D and ENF files can be opened.
Note: C3D files are stored internally after reading. So you can open the
same C3D before and after a change in different tabs and examine the results.
- Clear: Deselect all buttons of the current file.
- Stamp: Copy the selection status of the current to all
other file tabs. This means that the same variables are displayed for all open
- Tool (pocket knife): This is a
menu to call some tools and control the input and output:
- Info+ENF displays general trial information.
- To Workspace exports the current C3D as struct to
- Recent sessions opens the
momocd dialog to choose a session from the the list of recently
- Debug show problems at reading the C3D.
- Win explorer opens the folder of the current C3D in the
Windows explorer (or Konqueror on Linux).
- Blue background creates figure, which can look nicer on
- Show events toggles the visibility of event marks. This
can be performed through the context menu of the created figures also.
- Forces>Offset+Scale: The offset is removed from the
raw signals of the force plates and the results are scaled. This concerns the
X12 to Z4 channels.
- Forces>Auto Offset: The function for calculating
the forces tries to determine better offset values. Vicon WorkStation defines
the mean of the first 10 frames as offset, but this is not precise and sometimes
completely wrong. The quality of the calculated torsion Tz strongly depends on
the correct offsets.
- Forces>Lab reference system: The forces and the
center of pressure are transformed from the plate's to the lab's reference
- Forces>Noise limit: The torsion around the Z-axis
and the center of pressure are very sensitive to noise of the signals, if the
acting forces are small. Therefore the signals are set to zero if the force is
below a certain limit, e.g. 10 Newton.
- EMG: Auto offset:
The mean of the signals is usually a better offset for AD-sampling, than the
offset values written by Vicon WorkStation. Enabling this item enables the
mean-offset when the signals are filtered.
- X12 to Z4: Raw signals for
channels of Kistler plates (AMTI supported also).
- Fx, Fy, Fz, |F|, Tz: Components and length of the GRF
vector in the lab's reference system. Tz is the torsion around the plate's
Note: In MoMo "Fx" means the force in the current gait direction,
but in ShowC3D the global X-axis is meant.
- X, Y, CP: X-, Y-component and 3D point of the CoP.
- Filter icon: If enabled, force signals are filtered and
scaled. The sign of the value is not changed to allow for an easier comparison
with the raw signals. You can control the interpretation of the force signals by
some flags in the Tool menu.
- 1 to 16: Raw signals of EMG
channels. The recognition of EMG channels depends on lab specifix styles, which
are defined in
fC3D_UserDef. E.g. in the Gaitlab HD, the labels
of EMG channels start with "EMG " or "FW "
- Filter icon: Click on the icon to toggle filtering:
If enabled, the EMG signals are filtered by the user-defined filter selected
in the popup menu. (new: 04-Dec-2009)
See also: Tool>EMG: Auto offset.
- Note: Currently there is no way to display auxiliary channels:
analog channels which are neither forces nor EMGs. Please contact me if you
- Group, Parameter: The parameter in C3Ds are divided
into groups. Select a group at first. Right-click in the data field to toggle
the visibility of values.
- Labels: Select variables to be displayed. Shift and
Ctrl allows choosing multiple names, a right-click deselects all trajectories.
- 3D: Draw three 2D diagrams or a 3D plots for
trajectories. Use the mouse for spatial navigation in the 3D view.
- to 4D: Open trial in ShowC4D.
- sort: Sort labels alphabetically.
- Help: Show a help text. The HTML
button in the appearing dialog opens the HTML help page.
- Exit: Close the dialog, but not the created diagrams.
- Close: Close created diagrams, but not the dialog.
- Plot: Draw diagrams of selected variables and for
Some output diagrams contain event markers. They can be dragged vertically with
the mouse using the small arrow handle or text "Events" right from
the diagrams. A right-click on this handle toggles the visibility of vertical
lines through the events (new: 15-Jun-2010). If the event handle has vanished
after zooming into a diagram, disabling and re-enabling the events in the
context menu let them appear again.
If a curve contains (invisible) Inf or NaN values, the text 'Gaps!' is
displayed as warning. The context menu of this text (right-click) displays the
names of the affected trajectories. all frames with gaps are colored in light
yellow, if "Gaps" flag is enabled in the context menu of the diagram
or the figure.
Several jobs can be started through the context menu of the figures
(right-click) depending on the data: the visibility of gaps and events can be
toggled, values of the trajectories can be copied and
can be displayed.
The right-most icon in the toolbar toggles the visibility of the legend (do not
use the less powerful legend-icon of Matlab 7). The legend can be moved using
- Look at the tooltips (hold the mouse over an object for a while) for further
information, e.g. the path of the file.
- Buttons of not existing analog channels are disabled, e.g. for static trials.
- Open files from the command line:
FileName is a string or cell string.
- Use file patterns:
ShowC3D *16 opens e.g.
- The appearence, e.g. font size, is controlled by
can be changed in
- Clear all preferences, e.g. window positions:
ShowC3D('$version') or click on the title on the
- Dependencies from other tools (checked in
fC3D >= v5.01 (>= 5.13 preferred), GLToolbox >= v2.104.
- The initial values for the dialog, filters and parameters for processing
forces are defined in the file "ShowC3D.init".
This file can be edited manually. E.g. the number of force plates can be set
visualizes the contents of C3D files as
animated 3D objects. It can be called from the command line, from MoMoG or with
additionally created objects from the model scripts of MoMo.
The file and the ShowC4D-model can be defined as optional input arguments:
ShowC4D uses a model to identify markers and other objects in the variables
included in a C3D. These models are implemented as simple Matlab functions and
users can add own models
- Right, left and both (or middle) mouse key: similar
to method of Vicon-WorkStation.
- Open: Open a file. Right-click to open the file in a
- Play: It shows the current frame number and toggles
the status of running.
- Slider: Move the slider to select a frame. The events
are displayed above the slider. A right-click advances the current frame to the
- Solid 3D: Toggle solid or wire-frame mode.
- Floor: Show checkerboard floor.
- Grid: Visibility of grid on the walls.
- Markers: toggle visibility of markers.
- Uni tripods: Draw tripods with one color only,
or with X-, Y-, Z-axis in red/green/blue.
- Shading: Enable different shading modes.
- Renderer: Switch engine for drawing.
Auto let Matlab choose the renderer. If the hardware
OpenGL renderer fails, try software rendering with Generic
- Markers: Toggle visibility of markers.
- Projection: Select orthographic or perspective
- Group of view choices: Set camera and view-point
to the initial or default position, or look in the X-, Y- or Z-direction.
- New light: Move the light to the current camera
- Coordinates: Show axes of global reference system.
- Marker names: Attach labels to markers. This can
cause problems on export of graphics.
- Frame number: Display the current frame number or
time and events. The frame button on the bottom is not visible in exported
- Speed: Limit the animation frequency. With e.g.
"1/2x", the frames are drawn with an upper limit of the half recording
frequency. Nevertheless, the main limit is the prozessor speed, because
rendering in Matlab is slow. The speed of exported movies can be adjutsed
separately in the export dialog.
- Export: Export a graphics
file of AVI movie.
- Auto: ShowC4D selects the
model according to the marker set of the C3D.
- As markers: Display all variables as markers.
- List of models: A specific model can be chosen.
If none of the needed markers are found, a warning appears.
- ShowC4D Help: Display a help text.
- Size: Width and height of the output in pixels. For
JPEG and movie files this is set to multiples of 8 automatically. The minimum
width of Matlab figures is 104 pixels.
- Smooth: Anti-aliasing for nicer output.
- UI: Include buttons and slider in the output.
- Picture: Format: PNG files a recommended.
- Picture: Alpha: Transparent background for PNGs.
- Movie: Frame: Frame interval for saving.
- Movie: Format popup: Either AVI file or a series of
PNG files. PNG 8 creates files with an indexed color table with 256 colors. The
color-reduction is not stable – please vary the view point a little bit
and start the export again on problems. PNG 24 creates a series of true-color
pictures. The command for creating an animated GIF with ImageMagick is written
to the command window.
Specs opens a dialog
to specify the speed of the created movie and AVI properties as compression and
help avifile, Indeo5 at 90% quality creates a fair
- Save: Save picture or movie file.
Models for ShowC4D:
The relation between variables and 3D objects is defined in models, which are
implemented as simple Matlab functions. These functions are store in the
folder "ShowC3D4_Model", they can be modified and new models can be
created: Use the Model: Edit
menu. Then a new file is
created in the correct path. See the template file for help.
All versions 4.xy of
use the models in the folder
ShowC4D is not limited to C3D files as input. It accepts structs with a well
defined format (e.g. when called from MoMo). Further file types can be inserted
as plugins. Ask the author for help.
Reset the styles and window positions:
Arguments to show a trial with evaluation of MoMo:
The freeware program ImageMagick creates small and nice animated GIFs. The
needed command is written to the command line after the export of a movie as
series of PNGs.