Structured-light 3D scanner

A structured light 3D scanner is a 3D scanning device used to measure the three-dimensional shape of an object using a projected light pattern and a camera system.A light source from the scan head projects a series of parallel patterns onto the scan target.When light hits the surface of the object, the pattern deforms.A camera captures these images and sends them to 3D scanning software for processing.

Principle

Projecting narrowband light onto a three-dimensionally shaped surface produces a line of illumination that appears distorted from other perspectives than the projector and can be used for geometric reconstruction of the surface shape (light cross-section).A faster and more general approach is to simultaneously project a pattern consisting of many fringes or arbitrary fringes, as this allows a large number of samples to be acquired simultaneously.When viewed from different angles, the pattern appears geometrically distorted due to the surface shape of the object.A pattern of parallel stripes is widely used, although many other variants of structured light projection are possible.Image showing the geometric deformation of a single stripe projected onto a simple 3D surface.The displacement of the fringes allows precise retrieval of the 3D coordinates of any detail on the object's surface.

Generation of light patterns

Two main fringe pattern generation methods have been established: laser interferometry and projection.The laser interferometry method works with two broad planar laser beam fronts.Their interference results in regular, equidistant linetypes.Different pattern sizes can be obtained by varying the angle between these beams.The method allows precise and easy generation of very fine patterns with infinite depth of field.Disadvantages are high implementation cost, difficulty in providing ideal beam geometry, and laser typical effects such as speckle noise and possible self-interference of beam parts reflected by objects.In general, there is no way to modulate individual stripes, such as Gray codes.The projection method uses incoherent light and basically works like a video projector. Patterns are typically generated by passing light through a digital spatial light modulator, usually based on one of the three most widely used digital projection technologies today, transmissive liquid crystal, reflective liquid crystal on silicon (LCOS) or digital light processing (DLP; moving micromirrors) Modulators have various comparative advantages and disadvantages for this application. However, other projection methods can and have been used.The patterns generated by digital display projectors have small discontinuities due to pixel boundaries in the display.However, sufficiently small borders are practically negligible, as they will be flattened by the slightest defocus.

A typical measurement package includes a projector and at least one camera.For many applications, two cameras on opposite sides of a projector have been determined to be useful.Invisible (or imperceptible) structured light Using structured light does not interfere with other computer vision tasks where projected patterns would confuse.Example methods include using infrared or very high frame rates alternating between two diametrically opposite modes.