Weighted onorbit calibration method of principal point and focal length for star sensor

Distortion produced by optical system makes the image of object in linear CCD deviate from the theoretical point and lead to the system measuring error. According to the digital image processing, a high-precision calibration method is proposed. The imaging measurement system is calibrated through two steps: firstly, use laser collimation to detect the principal point for a large visal field camera lens with short focal distance. Secondly, use a rectangular gidding target to get lens distortion coefficient.

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A Stratified Optimization Method for Camera Self-Calibration

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.580.248 ◽

2012 ◽

Vol 580 ◽

pp. 248-252

Author(s):

Qian Sun ◽

Dong Xu

Keyword(s):

Aspect Ratio ◽

Accurate Result ◽

Focal Length ◽

Optimization Method ◽

Singular Value ◽

Optimization Approach ◽

Point Location ◽

Principal Point ◽

Self Calibration ◽

Value Decomposition

We present an efficient stratified optimization approach for self-calibration of a camera in the case that its focal length and the principal point location are unknown. Generally we can assume that the two views are of the same focal length, and the pixels are nearly perfectly rectangular, also it is possible to know the aspect ratio rather accurately. In our approach, we use singular value decomposition to solve a modified Kruppa Equation to derive the focal length with the supposition that the principal point is at the center of the image, and perform an exhaustive search for the principal point near the center of the image to minimize a cost function. We can get a much accurate result with the optimized principal point location.

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Catadioptric Optical System Design of 15-Magnitude Star Sensor with Large Entrance Pupil Diameter

Sensors ◽

10.3390/s20195501 ◽

2020 ◽

Vol 20 (19) ◽

pp. 5501

Author(s):

Yang Bai ◽

Jianlin Li ◽

Rongwei Zha ◽

Ying Wang ◽

Guangzhi Lei

Keyword(s):

Optical System ◽

Attitude Control ◽

Pupil Diameter ◽

Focal Length ◽

Field Of View ◽

Star Sensor ◽

Spherical Lens ◽

Entrance Pupil ◽

Secondary Mirror ◽

Entrance Pupil Diameter

The optical system is one of the core components for star sensors, whose imaging quality directly influences the performance of star sensors for star detection, thereby determining the attitude control accuracy of spacecrafts. Here, we report a new type of optical system with a catadioptric structure and a large entrance pupil diameter for a 15-magnitude star sensor. It consists of an improved Cassegrain system (R-C system), an aperture correction spherical lens group and a field of view correction spherical lens group. By embedding the secondary mirror of the R-C system into the output surface of the negative spherical lens of the aperture correction spherical lens group, the blocking of incident light is eliminated from the secondary mirror holder. After the structure optimization, the catadioptric optical system (COS) had a spectral range of 450 nm–950 nm, an entrance pupil diameter of 250 mm, a half-diagonal field of view of 1.4° and a focal length of 390 mm. By using theoretical calculations and experimental measurements, it was verified that the COS, with the ability to correct astigmatism, lateral color and distortion, can fulfill the detection of 15-magnitude dark stars.

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A real-time calibration method for the systematic errors of a star sensor and gyroscope units based on the payload multiplexed

Optik ◽

10.1016/j.ijleo.2020.165731 ◽

2021 ◽

Vol 225 ◽

pp. 165731

Author(s):

Zhongguang Yang ◽

Xiaocheng Zhu ◽

Zhiming Cai ◽

Wen Chen ◽

Jinpei Yu

Keyword(s):

Real Time ◽

Calibration Method ◽

Systematic Errors ◽

Star Sensor ◽

Time Calibration

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DoF-Dependent and Equal-Partition Based Lens Distortion Modeling and Calibration Method for Close-Range Photogrammetry

Sensors ◽

10.3390/s20205934 ◽

2020 ◽

Vol 20 (20) ◽

pp. 5934

Author(s):

Xiao Li ◽

Wei Li ◽

Xin’an Yuan ◽

Xiaokang Yin ◽

Xin Ma

Keyword(s):

Optical Axis ◽

Focal Length ◽

Calibration Method ◽

Depth Of Field ◽

Model Parameters ◽

Lens Distortion ◽

Camera Model ◽

Distortion Model ◽

Manual Adjustment ◽

Close Range

Lens distortion is closely related to the spatial position of depth of field (DoF), especially in close-range photography. The accurate characterization and precise calibration of DoF-dependent distortion are very important to improve the accuracy of close-range vision measurements. In this paper, to meet the need of short-distance and small-focal-length photography, a DoF-dependent and equal-partition based lens distortion modeling and calibration method is proposed. Firstly, considering the direction along the optical axis, a DoF-dependent yet focusing-state-independent distortion model is proposed. By this method, manual adjustment of the focus and zoom rings is avoided, thus eliminating human errors. Secondly, considering the direction perpendicular to the optical axis, to solve the problem of insufficient distortion representations caused by using only one set of coefficients, a 2D-to-3D equal-increment partitioning method for lens distortion is proposed. Accurate characterization of DoF-dependent distortion is thus realized by fusing the distortion partitioning method and the DoF distortion model. Lastly, a calibration control field is designed. After extracting line segments within a partition, the de-coupling calibration of distortion parameters and other camera model parameters is realized. Experiment results shows that the maximum/average projection and angular reconstruction errors of equal-increment partition based DoF distortion model are 0.11 pixels/0.05 pixels and 0.013°/0.011°, respectively. This demonstrates the validity of the lens distortion model and calibration method proposed in this paper.

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