As one of the key techniques of vision coordinates measurement, camera internal parameters calibration is regarded by
technologists and has been researched a lot. Based on the study of regular internal parameters calibration methods such
as plane calibration, two-plane calibration, vanishing points calibration, stereo calibration and so on, combined with the
requirement of large space vision coordinates measurement for camera internal parameters calibration, this paper brings
forward independent internal parameters calibration and virtual stereo calibration methods. A special calibration
equipment is used in independent internal parameters calibration to calibrate original points coordinates of camera and
distortion parameters of lens, and a virtual target board and bundle adjustment algorithm are used in virtual stereo
calibration to calibrate internal parameters. They can be used in large space vision coordinates measurement and get high
The precision circle target sub-pixel centroid location is one of the key factors of large space 3D coordinates
measurement. In this paper, the circle retro-reflective targets and optical targets used in large space 3D coordinates
measurement are analyzed, and the characteristics and applied fields of target sub-pixel centroid location algorithms such
as gray weighted and squared gray weighted centroid location algorithms which combine with bi-linear interpolation or
improved cubic convolution interpolation method, are discussed. The influencing factors and improving methods for
circle target location are also analyzed. These factors include the resolution of the CCD camera, image grab noise, the
size of targets, the choice of exposure time and threshold value, the noncoincidence of centroid and center of the ellipse
imaging targets, the distortion influence of deformational targets and so on. Based on these, proper compensating measures are brought out for the problems such as target choice and location, influencing factors and eliminating measures.
The precision of target sub-pixel centroid location directly affects the result of large scale vision 3D coordinates
measurement. This paper deeply studies the sub-pixel centroid location algorithm of retro-reflective targets and infrared
optical targets used in 3D coordinates measurement system, and makes use of improved cubic convolution interpolation algorithm to increase the number of effective pixels used in centroid location, then gives optimizing adjustment parameters for different types of targets and combined with squared gray weighted centroid location algorithm, finally realizes accurate target sub-pixel centroid location. This algorithm is proved to be effective and robust by simulations
A high accuracy and flexible method for calibrating intrinsic parameters of CCD camera is presented. The intrinsic parameters of camera is determined from collinear constraint and computed through bundle adjustment algorithm. Calibration is carried out by moving an optical feature point with CMM and forming a virtual stereo calibration board. The images of this virtual board are taken by the calibrated camera which in different locations and orientations. Due to take infrared LED as feature point and the light intensity of these feature points can be automatically controlled according to the distance between camera and feature point, the imaging feature points have uniform intensity profile and high contrast with background, and hence the calibration accuracy is improved. This method has been used for calibrating the Kodak MegaPlus 1.4i CCD cameras, which used in large-scale stereo vision coordinate online measurement system, and obtained higher measurement precision.
A 3-D coordinate measurement with novel concept and experimental arrangements of large space and multiple viewpoints is proposed. The measurement system includes a stereovision sensor and a separate LCD stripe projection. This measurement method ensures a high number of object points, up to 5x5x5m measurement volume, and rapid data
acquisition. If only one and next partial view have an overlap area, system could automatically transform each partial views measuring data into a same world coordinate system. It can measure a wider area or 360 degree (whole-body) shape by alter the stripe projection's position. Furthermore, it is unnecessary to stick any marker on the
object surface and a subsequent matching of the partial view is not required to obtain a whole-body measurement.
An optical probe imaging based, fully automatic and rather flexible stereo vision system for 3D coordinate on-line measurement is presented and analyzed. In this system, the relative position of the two cameras can easily be calibrated by observing an optical reference bar in different locations and orientations through the measurement according to epipolar constraint and the certified distance of the features on the reference bar. For measurement, the
system takes an optical probe, which has one reference mark and five optical feature points, as imaging target, and makes use of the measurement results of these feature points space coordinates to calculate the measured object point coordinate which contacts with probe tip. To improve the calibration and measurement accuracy, the system takes infrared LED as optical feature point, and optimized signal to noise ratio by automatic LED light intensity, located
these feature imaging points by bilinear centroid sub-pixel algorithm. The effectiveness of the proposed system has been test by experiments.
A new method for calibrating stereo photogrammetric system is presented. The relative position of the two cameras are determined from epipolar constraint and computed through linear normalization eight-point algorithm and M-estimator method. Calibration is carried out by moving a scale bar, which has six small infrared LED marks and the distances between these marks are used to determine the scale factor and the cross ratio invariant of the two distances between
the three marks on rigid reference bar is used to verify the matching quality. Due to take infrared LED as feature point and the light intensity of these feature points can be automatically controlled according to the distance between cameras and reference bar, the imaging feature points have uniform intensity profile and high contrast with background, and hence the calibration accuracy is improved. The simulations and experimentations have shown that the
calibration accuracy can be compared with complex off-line calibration.