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, so a pcurve fitted apart can report a tiny error and still evaluate far from its 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.