Function drum_onto_plane 

pub fn drum_onto_plane(
    plane: &Plane,
    cylinder: &Cylinder,
    tol: Tolerances,
) -> Option<Vector>

The move across a drum’s axis that lays its wall on a plane, where the two touch along a line to within the confusion distance: the axis parallel to the plane, and its distance from the plane within the confusion distance of the radius, either side, to the rounding that distance is read with. None otherwise.

Within that distance the drum and the plane are one configuration, the tangent one: the wall either side of the touching line stands off the plane by no more than the drum’s own depth past it, so a drum raised through the plane by a hair and one lowered short of it by a hair are told apart by nothing the tolerance can see. Every decision about the line reads this one answer: surface_surface meets the two along the one line, and a boolean computes the drum’s other sections on the drum moved by it, so that they end where the line does.