skeleton relationship

[ruddle]

Hey,

In my vizard, there are 27 skel_xxx under the Bones. I'd like to know the parent child relationship of all these bones. Where can I find this information?

Now I use censor to get the position of the hands. Is there any simple way to figure out the position of arms based on the position of hands?

Thanks.

[farshizzo]

Hi,

Here is the bone hierarchy for the standard Vizard avatars:

skel_Center
  skel_Pelvis
    skel_Spine
      skel_Spine1
        skel_Spine2
          skel_Spine3
            skel_Neck
              skel_Head
                skel_Jaw
              skel_ShoulderL
                skel_ArmLU
                  skel_ArmLL
                    skel_HandL
                      skel_HandLF
              skel_ShoulderR
                skel_ArmRU
                  skel_ArmRL
                    skel_HandR
                      skel_HandRF
      skel_LegLU
        skel_LegLL
          skel_FootL
            skel_FootLToe
      skel_LegRU
        skel_LegRL
          skel_FootR
            skel_FootRToe

In Vizard 3.0, you can determine this at run-time.

Vizard does not come with any inverse kinematics (IK) features. You will have to calculate this manually. Does your sensor only provide the position of the hand, or the orientation as well?

[ruddle]

My sensor only provide the position of the hand.

If I move the parent bone, does the child bone automatically move along with it? BTW, what's skel_HandLF? Finger?

Thanks.
ruddle

[farshizzo]

Hi,

The avatar skeleton is a hierarchical structure, so moving a bone will affect all children of that bone. The 'skel_HandLF' is the bone for the left hand fingers.

[ruddle]

Thanks.
Where can I find the information such as length of upper arm, fore arm?

[farshizzo]

Hi,

If you want to know the length of the upper arm you need to compute the distance between the shoulder bone and the elbow bone. For the forearm you will need to find the distance between the elbow bone and hand bone.

[ruddle]

Hi, I'm not sure how to calculate the distance between bones. I also want to calculate the distance from the elbow rotation axis to the shoulder, and the distance from the elbow rotation axis to the wrist. Do you have any code sample?

Thanks.

[farshizzo]

Hi,

You should be able to compute the distance between the bone positions to get the arm length. For example:

pos1 = shoulderBone.getPosition()
pos2 = elbowBone.getPosition()

length = vizmat.Distance(pos1,pos2)

[ruddle]

Thank you so much.

[ruddle]

Sorry, two problems when I use your code.

1. I guess shoulderBone comes from getbone('skel_ShoulderL'). Then where is elbowBone from? I don't see a elbow bone in the skeleton.

2. If shoulderBone and elbowBone are from getbone(), maybe because my Vizard is only 2.17a, it doesn't support <bone>.getPosition command. Is there any substitute?

More question about version 2.17a:
It seems <bone>.setEuler doesn't work in this version too. Any substitute for setting the rotation of the bone?

Thanks,
ruddle

[farshizzo]

Hi,

Sorry, the code I posted was for Vizard 3.0. In 2.17, I believe the syntax for getting a bone position/rotation is the following:

pos = bone.get(viz.POSITION)
euler = bone.get(viz.EULER)

If you want the length of the upper/lower arm, then I believe you should be interested in the following bones:

skel_ArmLU
skel_ArmLL
skel_HandL

[ruddle]

This time it works. Thank you.

The results are:
The distance between skel_ShoulderL and skel_ArmLU is 0.144409524884.
The distance between skel__ArmLU and skel_ArmLL is 0.159618362784.
The distance between skel__ArmLL and skel_HandL is 0.00597032904628.
So I guess the length of upper arm is 0.14, and the lower arm is 0.15. Right?

[farshizzo]

Hi,

Actually that's incorrect. You need to get the absolute world position of the bone:

bone.get(viz.POSITION,viz.ABSOLUTE_WORLD)

This should give you the following results:

skel_ArmLU -> skel_ArmLL = 0.284790087668
skel_ArmLL -> skel_HandL = 0.290760380194

[ruddle]

Many thanks. Two more questions about viz.ABSOLUTE_WORLD:

1. Given the angle between shoulder and upper arms, and the angle between upper and lower arms, Can I set the arm like this:

LowArmBone.rotate(0,-90,0)
UpArmBone.rotate(0,-60,30)

What do I need to use: viz.ABSOLUTE_WORLD or viz.ABSOLUTE_LOCAL?

2. Given the position of hand, Can I set the hand like this:

HandBone.translate(x,y,z,viz.ABSOLUTE_WORLD)

Why only viz.ABSOLUTE_LOCAL works?


ruddle

[farshizzo]

Hi,

viz.ABSOLUTE_LOCAL will perform the rotation in the bones local coordinate system. viz.ABSOLUTE_WORLD will perform the rotation in the world coordinate system. There were some bugs with performing manual bone rotations in Vizard 2.x. I would recommend upgrading to Vizard 3.0 if possible.

Translating the hand with viz.ABSOLUTE_WORLD should work. Are you locking the bone before performing the translation?

[ruddle]

Yes. I locked all bones from shoulder to finger.

Thanks,
ruddle

[mspusch]

It might be irrelevant, but Vizard R3 now can interface with Motionbuilder, which allows flawless and real-time integration of Mocap data from any Mocap system with the Vizard avatars. there are a bunch of videoclips at
http://www.worldviz.com/products/liv...ers/index.html