Markers Cluster in Visual3D - How Does it Work?

[Tomer Yona]

Hey everyone,

I was wondering if anyone knows how Visual3D treats a cluster of markers.
Does it do any math operations to reduce STA? or is it just used for better tracking because there is more chance to see the markers at each frame?

Lastly, does anyone know about a good book/online resources to learn visual 3D besides the online documentation website?

Thanks, and have a great week,
Tomer

[Dimitrios Menychtas]

Hello Tomer,

Your question is a bit general, but I'll try to answer as best as I can.

Visual3D uses three markers to define a segment and then adds any redundant marker you define to the same segment. It doesn't do anything that you'll not explicitly ask/code, so adding more markers to a segment does not make your results more accurate if the operation doesn't require them. That said, certain kinetic operations that use extra markers to define the segment's geometry rely heavily on them. Another way additional markers can be used is to define virtual markers in order to position your joint center and frame where you need it to be. Again, it's more about what you are trying to achieve, rather than any inherent benefit of the extra markers.

In general Visual3D is a post-processing tool, you should load c3d files after they have been properly reconstructed inside Nexus (or any other software your motion capture system uses). What I mean is that there shouldn't be any missing markers in the loaded trials at all, therefore you shouldn't rely on redundant markers to compensate for the missing ones once you start working in this software. In general, three markers for each segment should cover most basic kinematic operations.

Regarding the book you asked, there's "Research Methods in Biomechanics" by Robertson et al. that uses Visual3D a lot. Technically speaking, is an introductory text to biomechanics in general, but it heavily uses ( and teaches) the software.


I hope that helps,

Cheers
Dimitri