Function fit_surface_grid_at 

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

Fit a rectangular grid at fixed parameters: u_params[i] is the surface’s own u at rows[j][i], and v_params[j] its v.

The surface counterpart of fit_points_at: the caller’s chart is kept, which is what lets a replacement surface take over every pcurve drawn on the old one. As fit_surface_grid, rows first and columns second on shared knots, and the reported error is the surface against every input point at its parameters. Between the grid points the fit is not measured here; a caller holding the exact surface measures it there.

Errors

As fit_surface_grid, and the parameters must strictly increase and be one per row and one per column.