Function fit_surface_grid_at_with_knots 

pub fn fit_surface_grid_at_with_knots(
    u_params: &[f64],
    v_params: &[f64],
    rows: &[Vec<Point>],
    degree: usize,
    tolerance: f64,
    knots: (&'_ [(f64, usize)], &'_ [(f64, usize)]),
    tol: Tolerances,
) -> OgeomResult<Fitted<BSplineSurface>>

As fit_surface_grid_at, each direction’s knots starting from the interior knots given for it, (parameter, multiplicity), and keeping them. Where the chart the points come from is only C0 or C1 along a parameter line, a knot there of multiplicity degree or degree - 1 lets the fit turn as the chart does; without one, a fit smoother than its data converges on such a line only as fast as its spans shrink. A multiplicity past the degree counts as the degree, and a knot outside the parameters’ open range is not used.

Errors

As fit_surface_grid_at.