How do I move and rotate bones, parent relationships, etc.?

[adamkewley]

AK: This question was ported from [email protected] . Some details were REDACTED or edited because the original question was private.

I am trying to create a model of the anatomy that would replicate a rotationplasty surgery. So I need to move and rotate bones, their parent relationships, and the tendon insertions. I'm tempted just to edit existing xml model files. I certainly can see how this could be built from scratch with OpenSim Creator, but I feel like this is probably not the most efficient approach and just wondered if you had a thought.

[adamkewley]

I think the most common workflow that people follow for something like this is to edit the existing model files in a combination of OSC and an XML editor (depending on how confident you feel about osim XML, etc.) - it's designed with OpenSim compatibility and hot-reloading support exactly to support those kinds of hybrid workflows.

If you're already familiar with OpenSim GUI/OpenSim XML (osim) and just want to know where OSC might come in handy, then here's the key points that usually help users in that demograph (the tutorials are targeted more at people who haven't modelled before, etc.):

• OSC will auto-reload if you change the osim file "underneath it":
  • This means that you can edit the XML in one window and immediately see any changes in the GUI once you hit save.
  • everything in the UI should automatically update by design. This includes the log (handy for spotting XML errors) and the 3D renderer (for visualizing spatial changes)
  • And it also includes updating any live muscle plots (created by right-clicking a muscle, plot vs. coordinate, updates on any change), which is handy for fitting muscle parameters/paths etc. to experimental data (because you can always import an overlay from a CSV file over one of the plots - it'll stay there while the plots auto-update)
• Auto-reloading isn't limited to text editing, it also applies if (e.g.) you edit the osim file in the OpenSim GUI and hit save, which lets you use features from OpenSim GUI while still being able to use OSC
• OSC's spatial features are probably better than OpenSim GUI's, or XML, you'll find them useful if you're placing stations, muscle points, frames, etc. I've tried to make it such that:
  • The property editors show you what the spatial quantity is (i.e. as in the XML and OpenSim GUI)
  • But, where possible, there's custom UI code for customizing which coordinate system the spatial quantity is expressed in, which is handy if you're using different coordinate systems (e.g. CT scanner vs. ground vs. body)
• You can re-socket components by right-clicking then going to the "Sockets" menu
  • This is handy when you (e.g.) want to reattach exo devices, muscles, etc. to different bodies in the model
  • If the component being reattached is spatial (e.g. a frame, a station), then the UI also tries to detect that and shows a "re-express in new frame" option. This will perform the necessary maths to ensure your component doesn't move around when it's reattached elsewhere (because, as far as OpenSim's concerned, the position of those things is w.r.t. what they're attached to)

There's also handy little things like fitting analytic geometry, calculating things, etc. - I should probably write some more tutorials, update the tutorial videos, etc. but doing so takes time out of an otherwise quite busy development schedule!