index.md

layout: default
title: Active scanning
nav_order: 4
mathjax: true

Active scanning

{: .no_toc}

Table of contents

{: .no_toc .text-delta }

1. TOC {:toc}

Structured light

Structured light methods are actively projecting light patterns onto the scene, creating features that are easily detected by one or more cameras looking at it.

Laser line

A straightforward to introduce structured light to the scene is to project a line using a laser:

source: http://mesh.brown.edu/desktop3dscan/ch4-slit.html

The illuminated pixels are easily detected on the camera. For each illuminated pixel, the camera's intrinsic and extrinsic parameters can be used to obtain the cartesian equation a line on which the 3D point must lie. If the laser's plane cartesian equation is known through prior calibration, the intersection between that plane and the light ray is straightforward to compute.

After collecting 3D coordinates of each point on the illuminated curve, the object is moved or rotated, and more points are accumulated. Note that the rotation of the object must be precisely known in order to place the 3D points in the right context. In other words, the camera's extrinsic parameters must be accurately updated for each object pose.

source: http://mesh.brown.edu/desktop3dscan/ch4-slit.html

Encoded pattern

Projectors are a bit like reverse cameras: they use optics to project light rays onto the scene, rather than sensing them. The camera equations we previously presented are just as valid for projectors, and can be calibrated in a similar way. This also implies that the stereo vision principles can be applied to a projector/camera pair, rather than a camera/camera pair.

In projector-assisted structured light methods, easily detectable features are projected onto the scene, to be then detected by the camera and triangulated back to a 3D coordinate.