Function passes_a_pole 

pub fn passes_a_pole(
    curve: &Curve,
    surfaces: [&SurfaceGeometry; 2],
    reach: f64,
    tol: Tolerances,
) -> bool

Whether curve passes a pole of either surface’s chart within reach between its ends: nearer the pole than reach somewhere, its ends both farther.

A section fitted whole past a pole states a tolerance about its own distance from the pole, since no image follows the chart’s half turn there. Within that tolerance the pole is a point of the section as the fit states it, and the branch is cut there as cut_at_poles cuts it within the march’s chord.

The nearest approach is read at its worst among evenly spaced samples, refined by golden section between their neighbours.