Anyone know how we can measure the arc length around this 3D torodial shape (blue highlighted surface in img1)? I would like the arc length at the 1/2 depth of the groove. I can't find a way to split the surface and then measure the split edge since its a 3D curve/surface. img2 shows what I need the length of, but its in the wrong location as it is down at the bottom of the groove. img3 is a hand sketch of the arc length I'm interested in.
Thanks in advance.