Visual Measurement Method for Transparent Elements Based on Sub-Pixel Image Mosaics

Shilin Li; Songxin Dai; Zhongwen Hu; Hangxin Ji

doi:10.3788/LOP213351

Laser & Optoelectronics Progress, Volume. 60, Issue 6, 0615004(2023)

Visual Measurement Method for Transparent Elements Based on Sub-Pixel Image Mosaics

Shilin Li^1,2, Songxin Dai^1,2、*, Zhongwen Hu^1,2, and Hangxin Ji¹

¹Laboratory of Astronomical Spectroscopy and High Resolution Imaging, Nanjing Institute of Astronomical Optics &Technology, National Astronomical Observatories, CAS, Nanjing 210042, Jiangsu, China

²School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China

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Figures & Tables(13)

Fig. 1. System of visual inspection

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Fig. 2. Optical elements and gridding background

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Fig. 3. System error. (a) Installation error model of CCD; (b) imaging model with $α_{U, X}$

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Fig. 4. Calibration of coordinate system rotation angle. (a) Calibration of $α_{U, X}$ ; (b) Calibration of $β_{V, Y}$

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Fig. 5. Imaging model with $X_{W}^{'} Y_{W}^{'} Z_{W}^{'}$

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Fig. 6. Model of corner analysis

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Fig. 7. Schematic diagram of feature point matching based on sliding window

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Fig. 8. Filter of offset vector

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Fig. 9. Results of interior point screening

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Fig. 10. Optical element splicing. (a) Image acquisition; (b) image after removing background

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Table 1. Test results of offset vector

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Table 1. Test results of offset vector

No.	$T_{U}$	$T_{U}^{'}$	$Δ T_{U}$	$T_{V}$	$T_{V}^{'}$	$Δ T_{V}$
1	1.10	1.07	0.03	1.10	1.05	0.05
2	2.20	2.17	0.03	2.20	2.13	0.07
3	2.65	2.62	0.03	2.65	2.66	0.01
4	3.15	3.10	0.05	3.15	3.07	0.08
5	3.30	3.28	0.02	3.30	3.29	0.01
6	4.40	4.37	0.03	4.40	4.32	0.08
7	5.50	5.53	0.03	5.50	5.42	0.08
8	6.60	6.61	0.01	6.60	6.68	0.08
9	7.75	7.84	0.09	7.75	7.67	0.08
10	7.70	7.74	0.04	7.70	7.67	0.03
11	8.50	8.53	0.03	8.50	8.47	0.03
12	8.80	8.83	0.03	8.80	8.77	0.03
13	8.85	8.95	0.10	8.85	8.86	0.01
14	9.90	9.93	0.03	9.90	9.93	0.03
15	10.00	9.99	0.01	10.00	10.00	0.00

Table 2. Pixels per unit length compared at stitching and unstitched area

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Table 2. Pixels per unit length compared at stitching and unstitched area

No.	Stitching area	Unstitched area	Error
Average	218.87	218.79	0.12
1	218.89	218.78	0.12
2	218.74	218.80	0.05
3	218.93	218.78	0.15
4	218.71	218.82	0.10
5	218.82	218.85	0.03
6	218.93	218.76	0.18
7	218.74	218.70	0.03
8	218.94	218.71	0.23
9	219.02	218.82	0.20
10	218.94	218.85	0.08

Table 3. Comparison between visual measurement and manual measurement
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Table 3. Comparison between visual measurement and manual measurement
No. Artificial Visual
Average 19946 19946.86
1 19945 19943.88
2 19948 19949.07
3 19946 19948.35
4 19946 19944.82
5 19945 19948.21

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Shilin Li, Songxin Dai, Zhongwen Hu, Hangxin Ji. Visual Measurement Method for Transparent Elements Based on Sub-Pixel Image Mosaics[J]. Laser & Optoelectronics Progress, 2023, 60(6): 0615004

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