Marker flipping in Vicon Nexus 2.1.1

[Bernard]

Hello,

I am Bernard, and I am analysing 3D running using Vicon Nexus 2.1.1. During gap-filling, I experienced "jumping" of markers, such that instead of forming a smooth filled trajectory, I end up with zig-zag trajectories.

Let's use an example (see "Flipped" picture). When a gap is identified in "C7", using a pattern source of gap filling, Nexus identifies the next position of "C7" to be at my left tibial marker. So if I fill this gap, the trajectory will look like "C7-LTIB-C7", thus a zig zag. In nexus, there are four gap filling methods, when this happens, all four methods produce the same "fipped" outcome. "Flipped two image" shows me trying to gap fill pelvis markers, where nexus tries to inter polate (red line) a trajectory way out of line.

Flipped.JPGFlipped two.JPG

In Nexus, we need to reconstruct and label the trials. I have been advised that the issue is with the reconstruction of 3D trajectories. I have manipulated some parameters with respect to reconstruction, but to no avail.


Problems:

1) What adjustment can I make to the reconstruction and labelling to reduce the recurrence of this events.
2) when flipping occurs, what can I do to correct it. I have tried "unlabelling forward and backwards", and " deleting section and unlabelling forward and backwards" to little avail.

Any vicon pro users or Vicon staff assistance can troubleshoot for me?

Gratefully,
Bernard

[Bernard]

Re: Marker flipping in Vicon Nexus 2.1.1

I will create a reply based on what Vicon Support has assisted me with. This is a cut and paste. Many thanks Vicon support for the assistance. I will have a try. For all to share.

"In Nexus 2.1, the 'Pattern Fill' has two options or modes - an Auto-select and a manual-select. The auto-select decides which labelled marker has the best matching trajectory path, irrespective of what segment the gap and fill-markers are on. Using the manual option allows you to specifically select what marker trajectory you would like the gap fill to be based on, and thus gives you more flexibility if you don't want to use the auto-select option. Your example in 'Flipped 1' would have me suggest to manually select the T10 (or another marker on the torso) for use in the Pattern Fill.

I don't have information on how large your gaps are, but if I take 'Flipped 2' as an example, the pelvis marker that you are attempting to gap fill is incorrectly labelled at one section - the section circled in red in my attachment. Therefore when you attempt to fill the gap, it will currently fill it incorrectly and still give you a zig-zag./jumping type finish for the marker. This is also why the red spline fill line deviates to such a degree. It is important to ensure that the labelled marker trajectories are correct before gap filling otherwise erroneous fill patterns will be provided.

In this case, you need to adjust the section where the marker has been incorrectly reconstructed and labelled. The easiest way is to drag the cones at the the ends of that gap to the areas where the trajectory is correct (green arrow in attachment). Both the spline fill and pattern fill lines will adjust to accommodate this change in desired gap fill. I think with this adjustment the gap fill will be more acceptable for you. You could also delete that section of trajectory and then fill the gap, but I think the first method is easier."Flipped two_adjustment.JPG