Scaling: Max Marker Error and Visualizer Discrepancies

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Elizabeth Schmida
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Joined: Fri May 22, 2020 12:09 pm

Scaling: Max Marker Error and Visualizer Discrepancies

Post by Elizabeth Schmida » Sat Feb 13, 2021 10:23 am

Hi all,
I am working to scale several subjects using the GUI and I keep running into two issues regarding the max marker error. I have reviewed the scaling documentation, tutorials, and dug through previous forum posts, but have thus far had no luck finding an explanation. I am hoping to get clarification on the following discrepancies between the max marker error in the messages pane and the experimental and virtual marker offsets in the visualizer window:

(1) Of the 8 subjects I have scaled, all have a max marker error around 10cm, however, when I overlay the virtual and experimental markers in the visualizer window the markers are a good match (screenshot below). I think this may be a unit problem, but both the .osim file and .trc files specify the units as meters (sample files attached). Is there some other place units are specified, or something else I missed that would explain such a high marker error compared to what I am seeing visually? If not, which should I believe, the visual or the max marker error output in the messages pane?
Scaling_Shank_MarkerError.PNG
Overlaid markers
Scaling_Shank_MarkerError.PNG (295.65 KiB) Viewed 219 times
Messages Output: total squared error = 0.128967, marker error: RMS=0.056085, max=0.107094 (L.SH1)

(2) During scaling, regardless of the max marker error value, sometimes the identified marker doesn't seem to be the "poorest" match. For instance, if the messages pane identifies a left shank marker as having the max marker error, when I overlay the virtual and experimental markers and look at the whole model, the right shoulder markers look to have a greater offset. Similar to my first question, which should I trust, the output in the messages pane, or what I'm seeing in the visualizer window?

Any insight/suggestions into these discrepancies and how to proceed would be immensely appreciated! Thank you in advance for all the help!
Scaling_Sample_Files.zip
Scaling files (setup XML, static TRC, osim model)
(107.39 KiB) Downloaded 6 times

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