Questions regarding MoCap model

Main Forum
1

Is it necessary to have all four markers on the hip (RPSI, LPSI, RASI, LASI) in order for the model to run successfully? or is it possible to have only two hip markers? If it is possible to only use two hip markers, would I need to alter anything within the MoCap model script.

2

Hi,

If you have only two available markers for your pelvis segment,
there will be one missing information regarding the rotation about the axis which those two markers can create.

So in such a case, you should add one or two more extra drivers.

Maybe the easiest solution is to fix one of the three pelvis-thorax angles.

Best regards,
Moonki

3

Thanks for the response.

Do the two extra drivers need to be placed on the pelvis?

How would I set the pelvis thoracic angle? Is that in the trial specific file?

If one was conducting a lifting task, the pelvis would rotate therefore I presume I am unable to fix this angle. This correct?

Also, can foot markers be altered from the markers suggested from AnyBody and how many markers are necessary on the foot?

I am unfortunately losing too much visibility with the codamotion system I am using to capture 3D motion.

4

Hi,

In the ‘ExtraDrivers.any’ file in the Model folder of MoCapModel, you can find the following piece of code:

 AnyKinEqSimpleDriver PelvisThoraxDrv =
 {
     AnyKinMeasure& ref0 = ...BodyModel.Interface.Trunk.PelvisThoraxExtension;
     AnyKinMeasure& ref1 = ...BodyModel.Interface.Trunk.PelvisThoraxLateralBending;
     AnyKinMeasure& ref2 = ...BodyModel.Interface.Trunk.PelvisThoraxRotation;
     DriverPos = pi/180*
     {
         .JntPos.PelvisThoraxExtension,
         .JntPos.PelvisThoraxLateralBending,
         .JntPos.PelvisThoraxRotation
     };
     DriverVel =  pi/180*
     {
         .JntVel.PelvisThoraxExtension,
         .JntVel.PelvisThoraxLateralBending,
         .JntVel.PelvisThoraxRotation
     };
     Reaction.Type = {Off, Off, Off};
     //CType = {Soft, Soft, Soft};
 };

You can utilize this code to put some constraints between pelvis and thorax.

Of course fixing one of these three angles may not be the best solution. You may be able to introduce a kind of rhythm instead.

For foot markers, I would suggest you to use at least more than 3 markers.

Best regards,
Moonki