Data Export: C3D

C3D Export

Tracking data can be exported into the C3D file format. C3D (Coordinate 3D) is a binary file format that is widely used especially in biomechanics and motion study applications. Recorded data from external devices, such as force plates and NI-DAQ devices, will be recorded within exported C3D files. Note that common biomechanics applications use a Z-up right-hand coordinate system, whereas Motive uses a Y-up right-hand coordinate system. More details on coordinate systems are described in the later section. Find more about C3D files from https://www.c3d.org.

General Export Options

C3D Specific Export Options

C3D Axes

Common Conventions

Since Motive uses a different coordinate system than the system used in common biomechanics applications, it is necessary to modify the coordinate axis to a compatible convention in the C3D exporter settings. For biomechanics applications using z-up right-handed convention (e.g. Visual3D), the following changes must be made under the custom axis.

  • X axis in Motive should be configured to positive X

  • Y axis in Motive should be configured to negative Z

  • Z axis in Motive should be configured to positive Y.

This will convert the coordinate axis of the exported data so that the x-axis represents the anteroposterior axis (left/right), the y-axis represents the mediolateral axis (front/back), and the z-axis represents the longitudinal axis (up/down).

MotionBuilder Compatible Axis Convention

This is a preset convention for exporting C3D files for use in Autodesk MotionBuilder. Even though Motive and MotionBuilder both use the same coordinate system, MotionBuilder assumes biomechanics standards when importing C3D files (negative X axis to positive X axis; positive Z to positive Y; positive Z to positive Y). Accordingly, when exporting C3D files for MotionBuilder use, set the Axis setting to MotionBuilder Compatible, and the axes will be exported using the following convention:

  • Motive: X axis → Set to negative X → Mobu: X axis

  • Motive: Y axis → Set to positive Z → Mobu: Y axis

  • Motive: Z axis → Set to positive Y → Mobu: Z axis

Notes on Timecode Export

There is an known behavior where importing C3D data with timecode doesn't accurately show up in MotionBuilder. This happens because MotionBuilder sets the subframe counts in the timecode using the playback rate inside MotionBuilder instead of using the rate of the timecode. When this happens you can set the playback rate in MotionBuilder to be the same as the rate of the timecode generator (e.g. 30 Hz) to get correct timecode. This happens only with C3D import in MotionBuilder, FBX import will work fine without the change to the playback rate.

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