HELP

Ive uploaded a 3D model to help explain the situation. In reality the members (lines) in one direction will be in a different plane to the members running in another direction (3No. planes in total). I need to know the chord length and height of  every arc (so they can be fabricated). The trouble is the diagonals are not actually drawn as arcs (they are the surface lines of a torus). Is there a way i can convert these to arcs? Ive been trying to draw 3 point arcs on top of them, but it doesnt seem to be snapping to these lines correctly. It would be great if i could pull up an elevation of each arc also. Tried cutting a section but it says not cutting through any 3D objects. Thanks for any help

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Image may be NSFW.
Clik here to view.