Optics: measuring and testing – By polarized light examination – With light attenuation
Patent
1996-03-25
1997-10-21
Evans, F. L.
Optics: measuring and testing
By polarized light examination
With light attenuation
356371, G01B 1124
Patent
active
056802161
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a device for raster-stereographic measurement of body surfaces, preferably of irregularly shaped objects. The invention is used in particular for measuring parts of the human body or other biological objects or irregularly shaped technical component parts.
b) Description of the Related Art
In conventional raster stereography, a geometrical pattern of lines or dots is projected onto the surface to be measured and is recorded from a different direction by a camera, preferably a video camera, to which is connected a process computer. Two different principles are known for projecting raster lines. In the first principle, the line raster is achieved by line-scanning the surface with a light beam (described, for 515-529). The second principle was conceived by FROBIN and HIERHOLZER consists in a method for surface measurement by means of a projected grid containing periodically recurring lines of large thickness for a model reconstruction of the body.
A disadvantage in the method of raster stereography consists in that the entire pattern reflected by the surface being analyzed is recorded by the camera in one individual image. Although this enables a short recording time, the resulting image can be so complicated as to require a costly image analysis in order to coordinate or assign the image structures to the projected raster lines. This is indispensable for a correct model reconstruction of the body surface. For this reason, the density of the projected pattern must also not be too high, although a higher density would increase the theoretical resolution of the image. The maximum possible density depends on the surface shape, in particular on the depth modulation.
OBJECT AND SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to increase the possible scanning density without impeding the image analysis.
In a device for raster-stereographic measurement of body surfaces, preferably of irregularly shaped objects, in which a raster pattern having a plurality of raster lines is projected onto the surface according to the method of raster stereography by means of a raster projector and a line image which is distorted by the surface shape is recorded by means of a camera which forms a stereo base with the raster projector, this raster pattern having periodically recurring, particularly emphasized lines, where the order number of the lines can be deduced from the regular recurrence of these particularly emphasized lines, the object according to the invention is met in that the raster pattern which is projected on the surface contains locally modulated raster lines, wherein at least adjacent raster lines are clearly distinguished from one another. For this purpose, raster lines with periodic structures of different shape are advantageously used in the raster pattern (e.g., a diapositive).
Images of harmonic oscillations, as well as sawtooth modulation images or, in a particularly advantageous manner, square-wave modulation images are preferably used for this purpose. The oscillation images can be varied with respect to amplitude, frequency and/or phase position in order to obtain various distinguishable raster lines. When the raster lines have different phase positions relative to one another, the raster pattern is to be aligned substantially parallel to the stereo base to enable accurate analysis of the raster images in the camera picture. Further, the raster lines can be modified additionally or in a supplementary manner with respect to the light wavelength and/or the line thickness.
Further, unmodulated (straight) lines are advantageously inserted between modulated raster lines. Raster lines having a different modulation in pieces of lines are also suitable.
In order to maintain a clear distinction between the raster lines (so as to be substantially distinguishable from one another also with surface-induced distortion), the raster lines are advisably repeated sequentially within the raster pattern. Such seque
REFERENCES:
IEEE Transactions on Pattern Analysis and Machine Intelligence, 15 Jun. 1993 No. 6, New York, US, pp. 647-651 (Range Sensing by Projecting Multiple Slits with Random Cuts/Maruyama, et al.).
IBM Technical Disclosure Bulletin, 29 Apr. 1987, No. 11, Armonk, NY, USA pp. 4847-4848 (Color-Coded Light-Sectioning Method).
Drerup Burkhard
Hierholzer Eberhard
Aesculap-Meditec GmbH
Evans F. L.
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