Definition of segment reference frames from TLEM 2.0

[depierie (Enrico De Pieri)]

Happy New Year everyone!

I have a basic question to start this year.
I'm trying to extract position and orientation of all the lower-limb segments in the absolute reference frame in order to compare them with the kinematic definitions calculated from the conventional gait model in Vicon.
In order to do so I was planning to extract r and Axes for all the segments, but I need consistently-defined reference frames to compare the values.

I always assumed that the reference frame were implemented according to the paper by Carbone et al. documenting the TLEM 2.0 but it doesn't seem to match what's reported in the paper:

If I plot the segment reference frames in AnyBody
( for instance through:

Main.HumanModel.BodyModel.Right.Leg.Seg.Shank={
    AnyDrawRefFrame drw = {RGB = {1,0,0}; ScaleXYZ = {0.3,0.3,0.3};};};

but I also if I define a new RefNode in the segment with sRel = {0.0, 0.0, 0.0}; ),
I obtain the following reference frames:

They are potentially oriented like the ones described Carbone et al. but they definitely do not have the same origins, for instance the intra-malleolar point for the tibia.
I also read the Klein Horsman paper on the original TLEM 1.0 but I couldn't really find how these segmental origins are defined.

Can someone help me clarifying how the default segment reference frame are defined?

And to match the definition of the paper by Carbone et al, should I just define a new ref frame in the correct origin, while maintaining the same relative segment orientation?

Thank you!
Enrico

[melund (Morten Enemark Lund)]

Hi Enrico

I think the difference in position is because the model you are looking at is scaled.

You can disable scaling with

#define BM_SCALING _SCALING_NONE_

That will essentially give you the cadaver model. So now the segmental reference frames will be at the expected position.

Otherwise, if you need to use a scaled model then you can add the scaling function to the {0,0,0} position of the reference frame:

  Main.HumanModel.BodyModel.Right.Leg.Seg.Shank={
    AnyRefNode Test_Frame = {
      sRel = .Scale({0,0,0.0});
      AnyDrawRefFrame drw = {RGB = {1,0,0}; ScaleXYZ = {0.3,0.3,0.3};};
    };
  };

[depierie (Enrico De Pieri)]

Hi Morten,
Thanks for the .Scale({0,0,0.0} tip, that's exactly what I needed and the results make a lot more sense now.

Cheers,
Enrico

[Nickel_Lee (Li Hongwei)]

Hi Enrico

It is the Scaling problem as Morten mentioned above.

[melund (Morten Enemark Lund)]

@Nickel_Lee Sorry, I overlooked your message. I think it is the same. It is not really a problem, but just a consequence of the scaling being applied in a coordinate system which is different from the segmental reference frame.