musculoskeletal model OpenCap

[Francesca Zangaro]

Good evening.

I need to make a comparison between kinematics acquired with Vicon and with OpenCap. Since the comparison needs to be made on data that are based on the same model, I need to take the Vicon data to OpenSim, scale the model and calculate the inverse kinematics.
However, it seems to me that OpenCap is based on a 33 DOF musculoskeletal model that is not available on OpenSim and therefore I would not be able to create the "Vicon model".
So I am wondering how to proceed.

Thanks a lot!

[Matt Petrucci]

Hi Francesca,

The scaled model that you get from OpenCap is in OpenSim format (.osim), and should be in your folder when you download it.

What you could to do is take that model, open it in OpenSim, remove the markers, and then place the markers that you had from Vicon on that model, and then proceed with scaling, IK, etc.

Hope that helps,
Matt

[Francesca Zangaro]

Thank you for your reply.

I have another question about the coordinate system of OpenCap. I have read from literature that OpenCap uses the coordinate system of OpenSim: X forward, Y up, Z right. I noticed that in the folder of OpenCap that I downloaded there are the Calibration Images in which the coordinate system is different from that of OpenSim.

So I wonder if the marker trajectories are referred to the coordinate system of OpenSim (X forward, Y up, Z right) or if they are referred to the coordinate system in the Calibration Images.

Thanks a lot!
Francesca

[Edilson Borba]

Good morning

Now I have this doubt too. Below are images of the Opencap and Opensim systems

OpenCap


OpenSim

[Matt Petrucci]

Hi Francesca and Edilson,

The data are in the OpenSim convention.

Hope this helps,
Matt