problem with the contact geometry definition

[Linjie Wang]

Hi, there.

Is there anyone could help me?

Recently I built a knee joint musculoskeletal model in openSim, and trying to use the setting of triangular mesh volume (.obj) to define the contact relationship of knee joint. However, when I added the contact force in the forceset of osim file and ContactGeometrySet just as the attachments below, my contact geometry pair (left bottom one in the first screenshot) couldn’t be overlaid with my knee joint musculoskeletal model (right hand one). No matter how I changed the body name in the properties of Contact geometry (I guess the body name here is the local reference frame), the location and orientation of the contact geometry just didn’t have any change. So I am wondering if I misunderstood the local reference frame of the contact geometry or the setting I did is incomplete.

Thanks in advance,
Linjie

[jimmy d]

You will need to find the body frame of interest (femur?) and edit the location and orientation of your mesh relative to that.

I would suggest opening the model up in the GUI and using the navigator to toggling on the frames for the bodies. You will get a better idea of where each frame is and what values you will need to set for your contract geometries location and orientation.

Also, <body_name> should be the body that you are trying to connect your contact mesh to. So it should be something like femur_r (whatever the body name is).

[Linjie Wang]

Hi, James.

Thanks again for your reply.

Yes, I could find where those reference frames corresponding each body segment (femur and tibia) are.

The problems existing in my model are
a. My mesh geometries are far from the reference frames that the <body_name> are attached to seperately, even though the locations are set to be (0,0,0) under the properties of <body_name>. I dont know if the location and orientation are with regard to the local reference system of each body geometry that I can toggle on in the Nagigator as you just suggested.

b. When I reset the location to be (0,0,-1000), the mesh geometries do move closer to my musculoskeletal model but appear to be much greater than the latter one. Its quite strange that their sizes are that different, because my mesh geomeries (obj files) were produced from the same model (solidworks) that also produces stl files and those two kinds of files can be completely overlaid in the Meshlab.

Thanks,
Linjie

[Linjie Wang]

This problem has been sorted out. The contact mesh geometries can get overlaid with the musculoskeletal model now. The problem was caused by the third party software which automatically scaled my whole musculoskeletal model by 1e-3 times.