[auto-msk/subtalar joint] sphere fit on navicular needed

[modenaxe]

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We need a slightly different implementation for fair comparison with Montefiori et al JBiomech 2019.

[modenaxe]

A way of approaching this could be the following: taking the centre of the talo-navicular sphere and projecting it, along the subtalar axis, onto the navicular articular surface, identifying that surface, recompute the fitting sphere on that surface and recalculating the subtalar axis. What do you think @renaultJB ?

[renaultJB]

I think it's the way to go. An other possibility is to select all vertices on the navicular bone that lie within x mm of the talus articular surface, but it would require to tune this x value according to the size of the foot.

[modenaxe]

It should be relatively straightforward to identify the surface using a threshold of angle between the normal in that point and the face normals or (maybe better) identifying the points where curvature is maximum (borders of AS).

[renaultJB]

Yes, I also think it will be the easiest way, but I have not the geometry of the navicular in mind.