What are frames and sub frames?

When capturing data, the frame outputs are based on the capture rate of your Vicon hardware capture rate. You might be thinking to yourself “My camera system is capturing at 200Hz but my EMG/force plate/other device is capturing at a higher rate much higher than 200Hz!” Don’t panic, your data is all there.

In order to combine the varying data input capture rates Vicon Nexus uses Frames and Sub Frames. For example, you might have your Vicon cameras capturing at a rate of 200 Hz and an AMTI force plate capturing at a rate of 1000 Hz. If this were the case Vicon Nexus would use Frames based on the 200 Hz (200 frames/second) and Sub Frames based on the 1000 Hz (1000 frames/second). This would be the equivalent of 5 Sub Frames per Frame; ie. for every one frame of camera data there is 5 sub frames from the force platform.

If you were to export your device data in an ASCII the frame layout would appear as follows:

Frame
Sub Frame
1
0
1
1
1
2
1
3
1
4
2
0
2
1
2
2
2
3
3
4

You may wish to consider the sample rates for all devices being used in your system. When recording at multiple frame rates Vicon Nexus will up-sample data where necessary in order to ensure that the ratio between all data is an integer. For more information on up-sampling please see our guide here.

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