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Gap filling

Once you’ve labelled your markers, you may find that some of your marker trajectories have gaps where data is missing.
So in the cases where you’ve gone and done all of the labelling that you can and still you see that some of the markers do not have 100% of their trajectory filled, then this means that there are gaps in the trajectory. So these are our points where the markers were occluded or they went outside the capture space or something like this. And so the next stage of post-processing would be to go and identify those gaps, which in many cases will be visible on the– so in this editor by red marks or sort of blacked-out parts of the trajectory.
Yeah. So that you have a couple of choices for how to fill gaps, you can either do this in the software. Most of these softwares have some algorithms that you could use to fill the gaps where you’d choose to use some sort of interpolation. So you might choose to use a linear interpolation or a cubic interpolation. This depends on the type of movement that you’re expecting and also the length of the gap, the duration of the gap. And normally you don’t want to use an algorithm to fill gaps that are very large. So I don’t know what your personal cutoff point is. I kind of would often use around 50 milliseconds for most kinds of body movement.
If it’s something where the movement is elapsing very slowly, then maybe I would use a larger– a larger duration. But you don’t want to automatically fill a two-second gap because that’s– there’s quite some things that a person can do in two seconds and just guessing what they did is not very useful. So you can do this in the MoCap software but you can also do this after exporting this data into whatever analysis software you choose to use. You can use some kind of mathematical interpolation to fill the gaps. Another thing that you can do in some cases is use information from other markers to fill one gap. So I’ve done this sometimes with markers that are located on the torso.
So for instance, if you have a chest marker here and then you’ve got a couple of markers on the back, these tend to move quite in parallel. So if the gaps are located in the chest, you can use the information from the back markers to help you fill the gap that’s in the chest.

Once you’ve labelled your markers, you may find that some of your marker trajectories have gaps where data is missing.

There are different techniques available for filling gaps. Mari and Laura explain how the process of gap filling works.

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Motion Capture: The Art of Studying Human Activity

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