Function regular_grid_3d 

pub fn regular_grid_3d(
    origin: Vec3,
    nx: usize,
    ny: usize,
    nz: usize,
    dx: f64,
    dy: f64,
    dz: f64,
) -> Vec<Vec3> 

Build a uniform-spacing grid of points in 3D.

Returns points on a (nx × ny × nz) grid with spacing (dx, dy, dz) starting at origin.