the ground reaction force format

[Chunxia Li]

In the ground reaction force file, the format looks like this:

nColumns=19
inDegrees=yes
endheader
time ground_force_vx ground_force_vy ground_force_vz ground_force_px ground_force_py ground_force_pz 1_ground_force_vx 1_ground_force_vy 1_ground_force_vz 1_ground_force_px 1_ground_force_py 1_ground_force_pz ground_torque_x ground_torque_y ground_torque_z 1_ground_torque_x 1_ground_torque_y 1_ground_torque_z

my question is what does these items mean: ground_force_v?, ground_force_p?, 1_ground_force_?
????

I am working on ladder climbing activities, and i already have the motion data obtained by VICON system, but i don't have any force data. So I need to create some reasonable but fake ground reaction force. I need to consider both hands and feet, but during the ladder climbing process, the foot or the hand maybe in the air and not contact any part of the ladder, and the reaction force for this body part at this time should be 0. How to reflect this in the grf data that i am intending to create?

Thanks,

Chunxia

[Bingyi Long]

hi, Chunxia
As I kown, _v? represent force vecter、_p? represent foot's center of pressure and _torque_? clearly represent foot's ground reaction moment vector. The prefix of ground_ represent the right foot, correspondingly the
l_ground_ represent the left foot.


hope this help.
Bingyi

[Chunxia Li]

Thank you so much. In this case, the ground reaction force only considers feet force. How about the hands' force?

[Ayman Habib]

Hi Chunxia,

Regardless of the column labels (as long as they are unique), you need to specify what bodies on the model are these forces/moments applied to. The process is described on this forum thread
https://simtk.org/forums/viewtopic.php?f=91&t=3203

Please follow the steps described and let us know if you have questions. The new support page http://www.stanford.edu/group/opensim/s ... index.html
also contains a wealth of information regarding this and similar issues as well.

Best regards,
-Ayman

[Chunxia Li]

Hello Ayman,

Thank you so much. I think I understand your point. What if I want to have external load for both feet and both hands. In this case, ground_force_vx, ground_force_vy, ground_force_vz, and l_ground_force_vx, l_ground_force_vy, l_ground_force_vx are not enough. Because they can only be used for the feet or the hands. Not simultaneously for both of them. Do you know how to solve the problem here?

Thanks,

Chunxia

[Ayman Habib]

Hi,

As mentioned on the support site page
http://simtk-confluence.stanford.edu:80 ... Tutorial+3

The interface allows you to apply more than two forces e.g. column labels would be
ground_force_vx, ground_force_vy, ground_force_vz, and l_ground_force_vx, l_ground_force_vy, l_ground_force_vx, r_hand_force_vx, r_hand_force_vy, r_hand_force_vz, l_hand_force_vx, l_hand_force_vy, l_hand_force_vz and so on.

Hope this explains and best of luck,
-Ayman

[Chunxia Li]

Hi Ayman,

You mean I can add as many columns as I want to add? That would be awesome......

Chunxia

[Ayman Habib]

Yes, you sure can. Please let us know if you have questions following this approach.

Best regards,
-Ayman

[Michala Cadova]

Hi Chunxia,

I have now similar problem as you had – I need to define a “reasonable but fake ground reaction force”. I, more or less, understand the structure of the file, but I am not sure how to insert/chose/calculate the “center of pressure” for my bony part (the _p vector). How did you define it for the hand?

Thank for the reply
Michala