Abstract

Static laser scanning over a wide angle is demonstrated by ranging to 20 laser beams generated by a novel cylindrical quasi-cavity waveguide, using laser triangulation. Baseline distances and outgoing angles unique to each laser beam are calculated by modelling the triangulation arrangement using a system of linear equations and plotting principal rays. The quasi-cavity waveguide, imaging lens and focal plane are also plotted. The system is calibrated by finding optimal values for uncertain instrumental parameters using constrained non-linear optimization. Distances calculated over 5m indoors result in accuracies above 93%. Discrete laser spectroscopy using 640nm and 785nm laser diodes is also demonstrated. Both injected laser beams follow the same optical path through the quasi-cavity waveguide, enabling spectral measurements to be made from the same point on an object for both wavelengths. The reflected red and infrared laser light is digitally recorded by a CCD imager and differences in reflected intensity enable discrimination between various natural objects. This provides more complete information about the perturbing object, including its 3D coordinates as well as limited identification of its surface material.

© 2008 Optical Society of America

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References

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  1. K. Sahba, K. E. Alameh, C. L. Smith, and A. Paap, "Cylindrical quasi-cavity waveguide for static wide angle pattern projection," Opt. Express 15, 6 (2007).
    [CrossRef]
  2. L. F. Marshall, Handbook of Optical and Laser Scanning (Marcel Dekker Inc., 2004), Chap. 4.
    [CrossRef]
  3. A. B. Colquhoun, D. W. Cowan, and J. Shepherd, "Trade-offs in rotary mirror scanner design," Proc. SPIE 1454, 12-19 (1991).
  4. H. Horikawa, M. Miura, and T. Uchida, "Relationship between jitter and deformation of mirrors," Proc. SPIE 1454, 20-32 (1991).
  5. M. Hartrumpf and R. Munser, "Optical three-dimensional measurements by radially symmetric structured light projection," Appl. Opt. 36, 13 (1997), http://www.opticsinfobase.org/abstract.cfm?URI=ao-36-13-2923.
    [CrossRef]
  6. K. Sahba, S. Askraba, and K. E. Alameh., "Non-contact laser spectroscopy for plant discrimination in terrestrial crop spraying," Opt. Express 14, 25 (2006).
    [CrossRef]
  7. B. R. Myneni, F. G. Hall, J. P. Sellers, and A. L. Marshak, "The interpretation of spectral vegetation indexes," IEEE Trans. Geosci. Remote Sens. 33, 2 (1995).
    [CrossRef]
  8. R. B. Fisher and D. K. Naidu, "A Comparison of Algorithms for Subpixel Peak Detection," Sanz, ed., in Advances in Image Processing, Multimedia and Machine Vision (Springer-Verlag, 1996).

2007 (1)

K. Sahba, K. E. Alameh, C. L. Smith, and A. Paap, "Cylindrical quasi-cavity waveguide for static wide angle pattern projection," Opt. Express 15, 6 (2007).
[CrossRef]

2006 (1)

K. Sahba, S. Askraba, and K. E. Alameh., "Non-contact laser spectroscopy for plant discrimination in terrestrial crop spraying," Opt. Express 14, 25 (2006).
[CrossRef]

1997 (1)

M. Hartrumpf and R. Munser, "Optical three-dimensional measurements by radially symmetric structured light projection," Appl. Opt. 36, 13 (1997), http://www.opticsinfobase.org/abstract.cfm?URI=ao-36-13-2923.
[CrossRef]

1995 (1)

B. R. Myneni, F. G. Hall, J. P. Sellers, and A. L. Marshak, "The interpretation of spectral vegetation indexes," IEEE Trans. Geosci. Remote Sens. 33, 2 (1995).
[CrossRef]

1991 (2)

A. B. Colquhoun, D. W. Cowan, and J. Shepherd, "Trade-offs in rotary mirror scanner design," Proc. SPIE 1454, 12-19 (1991).

H. Horikawa, M. Miura, and T. Uchida, "Relationship between jitter and deformation of mirrors," Proc. SPIE 1454, 20-32 (1991).

Appl. Opt. (1)

M. Hartrumpf and R. Munser, "Optical three-dimensional measurements by radially symmetric structured light projection," Appl. Opt. 36, 13 (1997), http://www.opticsinfobase.org/abstract.cfm?URI=ao-36-13-2923.
[CrossRef]

IEEE Trans. Geosci. Remote Sens. (1)

B. R. Myneni, F. G. Hall, J. P. Sellers, and A. L. Marshak, "The interpretation of spectral vegetation indexes," IEEE Trans. Geosci. Remote Sens. 33, 2 (1995).
[CrossRef]

Opt. Express (2)

K. Sahba, S. Askraba, and K. E. Alameh., "Non-contact laser spectroscopy for plant discrimination in terrestrial crop spraying," Opt. Express 14, 25 (2006).
[CrossRef]

K. Sahba, K. E. Alameh, C. L. Smith, and A. Paap, "Cylindrical quasi-cavity waveguide for static wide angle pattern projection," Opt. Express 15, 6 (2007).
[CrossRef]

Proc. SPIE (2)

A. B. Colquhoun, D. W. Cowan, and J. Shepherd, "Trade-offs in rotary mirror scanner design," Proc. SPIE 1454, 12-19 (1991).

H. Horikawa, M. Miura, and T. Uchida, "Relationship between jitter and deformation of mirrors," Proc. SPIE 1454, 20-32 (1991).

Other (2)

L. F. Marshall, Handbook of Optical and Laser Scanning (Marcel Dekker Inc., 2004), Chap. 4.
[CrossRef]

R. B. Fisher and D. K. Naidu, "A Comparison of Algorithms for Subpixel Peak Detection," Sanz, ed., in Advances in Image Processing, Multimedia and Machine Vision (Springer-Verlag, 1996).

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Figures (7)

Fig. 1.
Fig. 1.

Basic principle of active laser triangulation.

Fig. 2.
Fig. 2.

Principal ray plot of the arrangement, showing outgoing and reflected rays, baselines, the quasi-cavity, lens and focal plane.

Fig. 3.
Fig. 3.

Experimental setup for active triangulation using the quasi-cavity.

Fig. 4.
Fig. 4.

The laser spot array produced by the quasi-cavity where (a) shows all 20 laser spots projected onto the perimeter and (b) shows spots 12-1.

Fig. 5.
Fig. 5.

Laser beam combination module.

Fig. 6.
Fig. 6.

Mean estimated distance measurement results. (a) shows the mean estimated forward range, Z, for 20 laser spots falling on the laboratory walls. (b) shows the mean estimated forward range, Z, for spots 12 to 16 projected onto the walls and spots 17–20 onto a perturbing screen.

Fig. 7.
Fig. 7.

Calculated S and NDI values.

Tables (1)

Tables Icon

Table 1. Optimized values for pixel scale factor η and camera rotation angle Lθ .

Equations (11)

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Z = f · x β x f tan ( w ) .
a = tan 1 ( C ( z ) S ( z ) C ( x ) S ( x ) ) .
w = tan 1 ( a L m 1 + ( L m · a ) ) .
β = ( β ( x ) L ( x ) ) ) + ( β ( z ) L ( z ) ) ,
β ( x ) = L b P b P m + L m ,
β ( y ) = ( P m · L b ) ( L m · P b ) P m · L m .
f ( x ) = a · e ( x b ) 2 2 · σ 2 ,
S = R ( λ k ) R ( λ j ) λ k λ j ,
NDI = R ( λ k ) R ( λ j ) R ( λ k ) + R ( λ j ) .
δ ̂ = 1 2 ln ( f ( x 1 ) ) ln ( f ( x + 1 ) ) ln ( f ( x 1 ) ) 2 · ln ( f ( x ) ) + ln ( f ( x + 1 ) ) ,
( Z i Z ̂ i ) 2 ,

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