Function fit_points_joint 

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

Fit one curve living in three spaces at once: a 3D curve and its two parameter-space images, as a single seven-dimensional fit.

One parameterization, one knot vector, one correction: the three results are same-parameter by construction, which separate fits cannot promise: each fit’s parameter correction drifts its parameterization independently, and the drift is invisible to every per-fit error measure. The boolean found that: pcurves claiming 1e-7 evaluated millimetres from their own curve. The reported error bounds the worst deviation across all seven coordinates, so it bounds each space’s deviation too.

Errors

As fit_points, and the three inputs must be equally long.