Each curve-type further describes how a 3D curve may be inferred as a stroke of that type. A common 3D curve inference results in the stroke being projected in 3D onto a minimum-skew viewplane. Given a 3D point P and direction D, the minimum-skew viewplane is the plane best aligned with the viewplane containing P and D as shown in grey, inset. This plane is readily computed as D×(R×D), where R is the ray from the eye to P.