Hi,
I've just started working with Anybody and I have the following questions:
I want to define some nodes on specific spinal vertebrae (C7, T9, T12, L1, L3, and L5). Based on what I found, each segment has its own specific coordinate. However, when I put the coordinate of each node on different segments like {0,0,0}, it seems all segments have the same coordinate (behind the pelvis). I’m wondering if I can define all the nodes relative to one segment like (C7) or put each node on different segments.
Does each node follow the movement of that segment and is always attached to that segment?
Assuming I defined the nodes separately on each spinal vertebrae, would the moment arm of these nodes relative to the L4-L5 disk node change over time? Are the nodes fixed to their respective segments, resulting in a constant moment arm relative to the L4-L5 joint during different activities (like walking, lifting,...)?
The origin of each segment (or segmental frame) depends mainly on how the stl files were generated. Typically, a part of the cadaver will be scanned and the scan will have a common origin for multiple bones. So, this is normal that when you find the origin by making a new node with sRel = {0,0,0} on a set of segments, they end up at the same point. This will happen, however, only in the neutral posture (or the posture in which the scan was made). If you want to capture the movement at the spine, please attach the reference nodes on the corresponding segment.
If you make the node on a specific segment, it will follow the movement of that segment and will always be attached to that segment.
Again, yes, if you make nodes on different segments, their distance to L4-L5 disc will change depending on the movement at the spine.
The only issue at the moment is that the entire thorax (T12 to T1) is modelled as a single rigid segment currently. So, there will be no relative motion between T9 and T12. However, we are currently working on a detailed thorax model that will be available in the future.