simtk.org

Hello,
I am using 6th Competition Data for my research. And I have some doubt about marker locations.
I am using SIMM for scaling of the generic model. I modified the markers name/position etc as given in the trc and marker pdf file. After scaling I can see good agreement between the SIMM markers and experimental markers. But then I observed some markers position are not same as given in Marker Set Description file (see attached image)
Also after scaling hip is getting rotated and I doubt this is because of twist in the knee markers. So it will be really helpful to have images (left side, right side, front & back) of the subject with all markers & with name, so that I can confirm whether the markers I have on generic model are on correct position or not. Also I can verify the scaled model visual quality?
There is an image (left & right view) with markers in Description document but it seems to be from earlier competition data and not having all the markers.
Looking forward to hearing from you soon...

Have a nice day!

Thanks & Regards
Priti Yadav

Dear Priti,

I'm afraid I don't have any photos to show you at the moment and can only refer you to Figure 1 of the Competition data description document, which you have seen already. I think the issue you are having may be partly related to the scaling process itself. Sometimes you have to iterate on your marker positioning to get satisfactory results after scaling (at least in my experience with OpenSim). A good check may be to perform inverse kinematics with a walking motion after scaling and look at your marker errors, then iterate until you reduce the model vs. experiment marker discrepancy to a satisfactory level.

Regards,

Ilan Eskinazi

Hello Ilan,
Thank you so much for your reply.
I think my question was not clear. During the scaling, it relates the distance between exp. markers (blue color in the image file) with model markers (pink color in image attached with last message). Or in other words it tries to fit the generic model within the experimental marker clouds. So if the model marker is overlapping the experimental marker (less rms error), then mathematically it will be considered as good scaling. The image I have attached with my earlier message, you can see there model markers (pink) and experimental marker (blue) are almost concentric. So it seems mathematically correct.
The doubt I have is about the experimental marker position like Thigh.Inferior marker position should be anterior, but it appears to be more lateral. Similarly Thigh.Lateral appears more anterior. Hence I wanted to see where exactly it was on the subject during experiment. Because that can help me to qualitatively verify my model and modify the segments orientation if required.
The Figure 1 doesn't show some of the markers (specially foot markers). It will be really helpful if you can provide even similar image as in Figure 1 but with all views (front, back, right side & left side view) and with all markers used in current competition data collection...

Have a nice day!

Thanks & Regards
Priti Yadav

Dear Priti,

Download the raw motion data and search for .avi files. There are some movies that show the marker locations. Photos and videos from all competitions should also help since the markers were always placed in the same manner for all subjects.

Regards,

Ilan Eskinazi

Thank you Ilan! I will look into the raw data...