Tools for graphically comparing the origin and insertion points of two models?

[mjhmilla]

I would like to graphically compare two models to see if they have the same origin and insertion points for a set of muscles. It is not straightforward to do this programmatically, because the models do differ: one model has a rigid upperbody, while the other has a flexible lumbar spine and a small rigid ribcage.

So far I haven't found a good way to visually compare these two models, but perhaps I'm missing something. In OpenSim Creator, is it possible to:

• Open both models in the same viewer and graphically overlay the two models?
• Open the models in two viewers side-by-side, and somehow copy the viewer settings?
• Or perhaps some other option?

Best regards,

Matt

[adamkewley]

@mjhmilla It isn't currently possible to open two models and overlay them in OSC right now because the core datastructure that the UI is based on is something like { Model; State; Hover; Selection; [WatchedOutputs] }. Changing it is going to require a higher-level datastructure (e.g. Environment { Models: [Model], Hover, [Selection], [WatchedOutputs] }. We've wanted to do it for a while but it isn't currently a thing 😦

The way I'd currently hack around this is to load the two models into OpenSim and play around with the offset setting in that (iirc)?

Longer-term, the intention is to provide direct rendering capabilities via Python in OPynSim. The underlying UI and rendering engine from OSC, including model rendering, has already been ported into it (all of the recent changes in OSC are related to this), the intention is that it'll provide a python API for grabbing the decorations, compositing them into one 2D image, and blitting it to the screen or an image file - loads of research projects have slightly different rendering requirements (incl. you!) so IMO it's the best place for it.

[adamkewley]

@mjhmilla actually, come to think of it, there's some other tricks you might be able to use, depending on your requirements:

• If you just need a single visualization and don't need live editing, you could export the model to a COLLADA DAE file and import it into Blender, which permits importing multiple scene files. You could then recolor it in blender for the comparison, if you just need one screenshot. The DAE exporter is hidden under the gear icon, right-hand side of each 3D visualizer panel.

• If you actually just want to match two moment arm curves, rather than the exact path (typical, if trying to match wrapping algorithms or similar), then you can create a live plot of the moment arm for the muscle (right-click, plot vs. coordinate, right-click plot, export CSV) and then open the other model, plot the same thing, and then right-click the plot and import CSV overlay(s), which will overlay the moment arm of the first model onto the moment arm of the second one. You can then edit the second model to match the moment arm.

• If you want to have both muscles in the same 3D scene and the model's basically the same, save for the muscle, you could also just manually copy the <MillardXXMuscle> component out of the XML of one and into the other, maybe give it a different name. Then you could go the the Muscle Styling button (top-left of each 3D visualizer) and select Appearance Property, then use the navigator panel to navigate to the copied-in-muscle's path subcomponent and give it a different color. This way, you'd have both muscles in one scene with two colors.

[mjhmilla]

Thank you very much, @adamkewley, for the fantastic response! Well beyond the call of duty - thank you!