What is the skeletal structure format of skeletonV*.ini?

[linzdg]

The skeletal structure format of skeletonV3.ini have something in common with BVH (BioVision Hierarchical). But the BVH defines each bone using keyword such as CHANNELS, OFFSET. In skeletonV3.ini defines each bone using keyword such as RPY_XYZ , DH . Is it possible to get the BVH format of icub skeleton?

[pattacini]

I presume you're referring to iCubGui conf files.

Maybe @ale-git can chime in.

[ale-git]

Yes, the iCubGui file format has been derived from the BVH format and adapted to our needs since the iCubGui was derived from a open source simple animation software. The main difference is that our format supports Denavit Hartenberg representation. We don't have the BVH format of the iCub model because the iCubGui was developed to read the already existing DH iCub model. BTW you can derive the BVH format from the iCub configuration file but it requires some effort.

[linzdg]

Hi , @ale-git I have some doubt that if DH( -15 -10.6 -90.0 90.0) ，then OFFSET(-15 0 -10.6). if RPY_XYZ( 0.0 0.0 -90.0 -21.6 -73.65 -60.5), then OFFSET (-21.6 -73.65 -60.5 0 -90 0). Is it correct to rewrite like this?

[ale-git]

Hi @linzdg , I'm not an expert about bvh files, but i think that the OFFSET parameters represent cartesian displacements (links). There are no explicit rotation offsets because the rotation angles are stored apart in the MOTION section. Here a document that explains the BVH format:

http://www.dcs.shef.ac.uk/intranet/research/public/resmes/CS0111.pdf

Hope this helps

[pattacini]

Closing, feel free to open it up again if needed.

[linzdg]

Now I have obtained the bvh file of iCub. And after retarget the human motion, I obtained the MOTION section of icub, is there any way to apply to the true robot and let it move？The Motion section consisits of euler angle of each joint, but Cartesian Interface of the positionMove needs the encoder data.

[ale-git]

The Dynamic Interaction Control group https://dic.iit.it/ is working on mimic, maybe they have some modules that translates from human body measures to robot joint space?

[pattacini]

Hi @linzdg

What exactly do you mean when saying "Euler angle of each joint"? A single revolute joint can only be commanded by asking it to move to a specified standard angle. Euler angles serve to determine orientations in 3D of a structure like a kinematic chain (for example the robot arm), not a joint.

The Cartesian Interface is a component that lets you control the pose of the end-point of a kinematic chain (for example the hand of the robot arm), thus comprising its orientation. The Cartesian Interface doesn't resort to positionMove of the joint as it commands the whole structure in the operational space. Therefore, the joints are moved by the algorithm itself.

To sum up, you ought to work in the joint space and come up with a suitable sequence of joint positions moving over time according to the format that is compatible with the output of yarpdatadumper. Once done with that, to replay the sequences on the robot you can make use of the dual component yarpdataplayer.

[linzdg]

BVH MOTION arrays provide Zrotation Xrotation Yrotation values which are Euler angles in degrees corresponding to the skeleton information defined above. For example, I want to use this Zrotation Xrotation Yrotation values to make left leg move. But no method was found to apply to icub. Here's the data I got from retargetting.

HIERARCHY

ROOT Hips
{
    OFFSET 0.000000 0.000000 0.000000
    CHANNELS 6 Xposition Yposition Zposition Zrotation Yrotation Xrotation 
    JOINT base_to_left_leg_1
    {
        OFFSET 0.000000 0.000000 0.000000
        CHANNELS 3 Zrotation Yrotation Xrotation
        JOINT 0_left_leg_fwd_2
        {
            OFFSET 6.810000 -11.990000 0.000000
            CHANNELS 3 Zrotation Yrotation Xrotation
            JOINT 1_left_leg_spread_3
            {
                OFFSET 0.000000 0.000000 0.000000
                CHANNELS 3 Zrotation Yrotation Xrotation
                JOINT 2_left_leg_rot_4
                {
                    OFFSET 0.000000 -24.000000 0.000000
                    CHANNELS 3 Zrotation Yrotation Xrotation
                    JOINT 3_left_knee_fold_5
                    {
                        OFFSET 0.000000 -22.000000 0.000000
                        CHANNELS 3 Zrotation Yrotation Xrotation
                        JOINT 4_left_ankle_pitch_6
                        {
                            OFFSET 0.000000 0.000000 0.000000
                            CHANNELS 3 Zrotation Yrotation Xrotation
                            JOINT 5_left_ankle_roll_7
                            {
                                OFFSET 0.000000 -4.100000 0.000000
                                CHANNELS 3 Zrotation Yrotation Xrotation
                                End Site
                                {
                                    OFFSET 0.000000 0.000000 0.000000
                                }
                            }
                        }
                    }
                }
            }
        }
    }

MOTION
Frames: 408
Frame Time: 0.008333
1.264031 65.080997 -8.960823 3.084827 13.962112 -7.686169 3.755391 -3.438108 -3.234098 4.267096 -2.626119 -1.939569 4.448896 -2.948539 -2.282182 -16.827582 -5.937031 16.566146 21.777096 14.325650 13.662276 24.228061 -1.332077 13.248087 0.000000 0.000000 0.000000

(The first three are Xposition Yposition Zposition of ROOT Hips)

[pattacini]

As said previously, you can command iCub either in joint space by streaming out joints set-points or in the operational space through the use of specific IK components like the Cartesian and Gaze interfaces.

[pattacini]

Closing, feel free to open it up again if needed.