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Methods of Acquisition

Laser Ranging Systems

Laser ranging works on the principle that the surface of the object reflects laser light back towards a receiver which then measures the time (or phase difference) between transmission and reception in order to calculate the depth.

Most laser rangefinders:

Structured Light Methods

Basic idea:

Moire Fringe Methods

The essence of the method is that a grating is projected onto an object and an image is formed in the plane of some reference grating as shown in Fig. 6.

The image then interferes with the reference grating to form Moire fringe contour patterns which appear as dark and light stripes, as demonstrated by Fig. 7. Analysis of the patterns then gives accurate descriptions of changes in depth and hence shape.


Fig. 6 A moire projection system


Fig. 7 Moire fringe patterns

NOTE: Ambiguities arise in interrogating the fringe patterns.

Moire fringe methods are capable of producing very accurate depth data (resolution to within about 10 microns) but the methods have certain drawbacks.

Shape from Shading Methods

Methods based on shape from shading employ photometric stereo techniques to produce depth measurements.

Using a single camera, two or more images are taken of an object in a fixed position but under different lighting conditions.

By studying the changes in brightness over a surface and employing constraints in the orientation of surfaces, certain depth information may be calculated.

Methods based on these techniques are not suited for general three-dimensional depth data acquisition:

Passive Stereoscopic Methods

Stereoscopy as a technique for measuring range by triangulation to selected locations in a scene imaged by two cameras already -- further details on general stereo configurations in Books.

The primary computational problem of stereoscopy is to find the correspondence of various points in the two images.

This requires:


Active Stereoscopic Methods

The problems of passive stereoscopic techniques may be overcome by

next up previous
Next: Our Active Stereo Vision Up: 3D imaging Previous: Introduction to Stereo Imaging

tex2html_wrap_inline2984 David Marshall 1994-1997