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Research Papers

Algorithms for Generating Adaptive Projection Patterns for 3D Shape Measurement

[+] Author and Article Information
Tao Peng

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742pengtao@umd.edu

Satyandra K. Gupta

Department of Mechanical Engineering, and Institute for Systems Research, University of Maryland, College Park, MD 20742skgupta@eng.umd.edu

J. Comput. Inf. Sci. Eng 8(3), 031009 (Aug 21, 2008) (12 pages) doi:10.1115/1.2956992 History: Received July 31, 2007; Revised March 12, 2008; Published August 21, 2008

Point cloud construction using digital fringe projection (PCCDFP) is a noncontact technique for acquiring dense point clouds to represent the 3D shapes of objects. Most existing PCCDFP systems use projection patterns consisting of straight fringes with fixed fringe pitches. In certain situations, such patterns do not give the best results. In our earlier work, we have shown that for surfaces with large range of normal directions, patterns that use curved fringes with spatial pitch variation can significantly improve the process of constructing point clouds. This paper describes algorithms for automatically generating adaptive projection patterns that use curved fringes with spatial pitch variation to provide improved results for an object being measured. We also describe the supporting algorithms that are needed for utilizing adaptive projection patterns. Both simulation and physical experiments show that adaptive patterns are able to achieve improved performance, in terms of measurement accuracy and coverage, as compared to fixed-pitch straight fringe patterns.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a PCCDFP system with one projector and one camera

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Figure 2

Measurement of a sphere using straight sinusoidal fringes with fixed pitch. (a) Sinusoidal fringe pattern (shown with uniformly increased fringe pitch than actual). (b) Image (portion view of the sphere under the projection of the pattern.

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Figure 3

Measurement of a sphere using curved fringes with spatially varying pitch. (a) Adaptive pattern (shown with uniformly increased fringe pitch than actual). (b) Image (portion view) of the sphere under the projection of the pattern.

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Figure 4

Schematic diagram of the measurement workflow when fixed-pitch fringe pattern is used

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Figure 5

Schematic diagram of the measurement workflow when adaptive projection pattern is used

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Figure 6

An example of the construction of generalized projection pattern. (a) Phase function Φ(ξ,η) (gray-levels represent phase values). (b) Projection pattern constructed, I(P)(ξ,η).

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Figure 7

Generation of an adaptive projection pattern for the measurement of a sphere. (a) Contours of the sphere's phase map, Φ(V) (pixels with large phase gradients, ∣∇Φ∣u, are highlighted. (b) Pixels in the projection pattern whose phase gradients, ∣∇Φ∣ξ, need to be set smaller than their initial values. (c) Contours of the constructed phase distribution of the adaptive pattern, ΦP(A). (d) Adaptive pattern generated at the end (shown with uniformly increased fringe pitch than actual).

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Figure 8

Construction of new reference phase map for an adaptive pattern. (a) Contours of phase map ΦR(V) (blue crosses are example pixels in the (u,v) space). (b) Contours of phase map ΦR(H) (example pixels drawn in blue crosses). (c) Phase distribution of the adaptive pattern shown in contours, ΦP(A) (red crosses are points in the (ξ,η) space that correspond to the example pixels shown in (a), (b) and (d). (d) Contours of the new reference phase map computed, ΦP(A) (example pixels drawn in blue crosses).

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Figure 9

Part with a cone-shaped hole

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Figure 10

One of the images acquired (portion view) by using fixed-pitch fringe pattern, nF=100

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Figure 11

Simulated measurement of a cone-shaped hole using adaptive fringe pattern. (a) Adaptive fringe pattern generated (shown in larger fringe pitch than actual). (b) One of the images acquired (portion view).

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Figure 12

Results of the measurement of a cone-shaped hole. (a) Point cloud obtained by using fixed-pitch fringe pattern, nF=100 (pseudo-color represents z-coordinate. (b) Point cloud obtained by using the adaptive fringe pattern. (c) Measurement performance: adaptive fringe pattern vs. fixed-pitch patterns (nF represents fringe number).

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Figure 13

Simulated measurements of a part with a sawtooth profile. (a) Part with a sawtooth profile. (b) Adaptive fringe pattern generated (shown using larger fringe pitch than actual). (c) Point cloud obtained by using the adaptive fringe pattern (pseudo-color represents z-coordinate). (d) Measurement performance: adaptive fringe pattern vs. fixed-pitch fringe patterns.

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Figure 14

Simulated measurements of a spherical surface. (a) Spherical surface. (b) Adaptive fringe pattern generated (shown in larger fringe pitch than actual). (c) Measurement performance: adaptive fringe pattern vs. fixed-pitch fringe pattersn.

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Figure 15

Simulated measurements of a spline surface. (a) Randomly generated spline surface. (b) Adaptive fringe pattern generated (shown in larger fringe pitch than actual). (c) Measurement performance: adaptive fringe pattern vs. fixed-pitch fringe patterns.

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Figure 16

Measurements of a plastic flowerpot. (a) Photograph of the flowerpot. (b) Adaptive fringe pattern generated. (c) Measurement coverage achieved: adaptive pattern vs. fixed-pitch fringe patterns.

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Figure 17

Measurements of a plastic tube. (a) Photograph of the tube. (b) Adaptive fringe pattern generated. (c) Measurement performance: adaptive fringe pattern vs. fixed-pitch patterns.

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Figure 18

Measurements of a plastic human face model. (a) Image (trimmed) acquired using fixed-pitch fringe pattern. (b) Adaptive fringe pattern generated (shown in larger fringe pitch than actual). (c) Image (trimmed) acquired using adaptive pattern.

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Figure 19

Measurements of a plastic base of a telephone handset. (a) Image (trimmed) acquired using fixed-pitch fringe pattern. (b) Adaptive fringe pattern generated (shown in larger fringe pitch than actual). (c) Image (trimmed) acquired using adaptive pattern.

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