A system and method are disclosed for controlling physical access through a digital certificate validation process that works with standard certificate formats and that enables a certifying authority to prove the validity status of each certificate C at any time interval starting with C’s issue date, D1. The client-side software application collects usage data and generates a user profile based on usage data. In a secondary separation step, secondary air is blown toward the raw grains dropping into the conical section in the primary separation step to blow the contained lightweight substances upward to the space in the cylindrical section. The second stage has first and second inputs connected to the first and second outputs of the first stage, respectively. In addition, a Z height extrapolation based on the Z heights of previous edge points can significantly speed up the searching process, particularly for objects where the Z height change of a contour is gradual and predictable.