Discussion and Support for the OptiTrack, SmartNav and TrackIR brands by NaturalPoint

Tracking Tools C3D Export - Tech Note

by Birch » Thu Jun 03, 2010 6:34 pm

Tracking Tools Tech Note
C3D Export Support
Minimum Tracking Tools version required : 2.2

- Data format is Signed Real, PC format.

- Only 3D Point data is exported.

- C3D supports only 255 labeled markers. For marker counts above this limit, data will be present in the file, but labels will not be preserved so access will need to be by index, as per C3D spec.

- Current marker limit is 500.

- Marker Labeling conventions:
- For Trackable-associated markers: TrackableName_MarkerLabel (e.g. Trackable1_1)
- For non-associated markers : MarkerLabel (e.g. 1051)

- Markers are listed in the C3D file in the following order:
1. Trackable-associated markers, in the order listed in TrackingTools.
2. Unassociated/Untracked markers.

- Tools create new marker labels for each newly detected marker (marker without known trajectory).
Every labeled marker will be present in the C3D file for the entire duration of the capture.

- For frames where a Marker's position is not observed, The C3D Residual value will be set to -1.0, as per C3D spec.
Otherwise, the Residual value is unused (0.0). In addition, the marker's position values will be set to

- Tools has the following options when exporting C3D data (In Tools -> App Settings -> Options -> C3D Export Options)
- Units (default is same as Tools - meters)
- Coordinate System mapping (default is same as Tools)

C3D files have been tested for compatibility with the following software:
- CMotion Visual3D (note : The Visual3D free viewer re-sorts marker lists alphabetically)
- MotionLabs MLS Viewer
- MotionBuilder 2010/2011
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by Boost » Wed May 04, 2011 4:37 pm

May we get a link to see a C3D motion file as exported from Tracking Tools?
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by NaturalPoint - Mike » Thu May 05, 2011 12:35 pm

I have a quick take I made with a few demo rigid bodies I can send you in both c3d and csv for comparison. Please email and I will reply with them.
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by litch09 » Sun Sep 16, 2012 9:02 pm

I have a question about the frame rate output to the C3D file format. This is obviously the average frame rate, however there are times when frames are missed (e.g. when driving with external sync in) or frame rate slows. Is it possible to include the timestamp (as in the CSV export) somewhere in the C3D file format?
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by NaturalPoint - Mike » Mon Sep 17, 2012 11:43 am

Not a bad idea. I've submitted this to our developers for review for future implementation.
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