Function fit_points_joint_from_held 

pub fn fit_points_joint_from_held(
    points: &[Point],
    on_a: &[Point2],
    on_b: &[Point2],
    stations: &[usize],
    closed: bool,
    degree: usize,
    tolerance: f64,
    tol: Tolerances,
) -> OgeomResult<(Fitted<BSplineCurve>, BSpline2d, BSpline2d)>

As fit_points_joint_from, splitting a span only where samples lie strictly inside it on both sides of the new knot.

The refinement splits a span between its two middle samples. Where a span holds two samples, one on its own start knot, that leaves a span whose only sample sits on its knot: nothing holds the cubic inside it, and the fit can pass every sample and swing between two of them by far more than their spacing, a turn round a drum in its chart image between samples a fraction of a millimetre apart. Here such a span is left whole and the fit stops there, its residual stated as it is.

Errors

As fit_points_joint_from.