Positioning And Measurement Techniques With Zoom Tracking Cameras

Zoom optical imaging systems like zoom cameras, photogrammetry cameras, PTZ cameras and optical theodolites are optical systems with their focal lengths can be continuously adjusted in certain extent for acquiring appropriate images of objects when the objects distance changes along the optical axis of the systems. Currently zoom optical imaging systems have been validly used in photography, photogrammetry, safety monitoring, vision tracking and high precision measurement areas.In the civilian photography, vari-focus lens have been taken place of the well-known fixed-focus lens and become the important part of the photographic cameras. In panorama photography, multiple single-images can be stitched into a large full view of panorama picture through rotating vari-focus lens around perspective projection center or called as the no-prarllax point (NPP). In vision tracking and navigation area, Pan-Tilt-Zoom(PTZ)cameras, whose azimuth angle, tilt angle and zoom ratio are adjustable, are used to track target with keeping the images size and imaging resolution constant, and to obtain the target’s orientation and positions. It is apparent that the research on the theoretic and technical issues of the vari-focus optical system and their imaging process has important academic and application values.In machine vision, the visual model parameters of fixed-focus optical image system are fixed in applications. The requirements for the model parameters’calibrations are to measure and estimate the values of the corresponding constant terms. For zoom optical image systems consisting of vari-focus lenses, however, the model parameters vary with the configuration setting adjust, and it is a big challenge to use zoom optical image system to implement tracking, position and measurement. The dissertation, which are supported by national863program, are concentrated on investigating some key scientific and technological topics in application of zoom optical imaging system for high precision tracking, positioning and measurement. The important research work and achievements in the dissertation are listed as follows:(1)The pinhole model and thick lens models of zoom optical imaging systems are investigated and summarized to understand the change rule of model parameters of the zoom optical imaging systems affected by zoom (focal length), focus and iris. The research results shows that thick model is better to model the zoom optical imaging systems with higher accuracy。(2) The physical positions of perspective projection center of the pinhole model of zoom optical imaging systems, and image centers are studied through theoretical analysis and experimental verification. The research results demonstrate that the perspective projection center is right at the intersection point between the entrance pupil of vari-focus lens and the optical axis in modeling the zoom optical imaging system. The image center is reasonable to be defined by the image point on the image plane intersecting by the perpendicular line from perspective center to image plane. To obtain high accuracy visual model, the entrance pupil of vari-focus lens are needed to keep constant in zooming. The conclusions offer theoretical supports for setting up a high precision zoom optical imaging system and modeling the system in high precision tracking, positioning and measurement.(3) The methods of tracking, positioning and measuring an object using PTZ cameras with change of their zoom (focal length), focus and iris are researched. The research involves establishing the numerical expression of the3D vision model with internal and external parameters adjustable and the model coordinate systems including global coordinates, PTZ coordinates about horizontal and tilt rotation, camera coordinates.(4) A six-dimensional (6D) measurement techniques and system based on PTZ cameras have been developed. A zoom tracking visual measurement setup has been built up for research on the topics of the zoom tracking, positioning and measurement. The setup consists of an auto-focus zoom tracking camera, a6freedoms probe with a standard sphere, whose surface is covered by pseudorandom color codes, and a computer. The pseudorandom color codes are distributed on the sphere with color arrays of holes, where color LEDs lighter are assembled. The hole arrays with the known center coordinates are used as a3D calibration target for the tracking system parameters self-calibration. Each hole position is recognized using the color emitted by its LED. The6D information of the probe is obtained based on the coordinates of the color array in the system coordinates. The tracking measurement setup has good potential application prospects in combination measurements and large equipment assembly process.(5)The methods and algorithms of recognizing the basic geometric features, such corner, line, ellipse and etc. in zoom vision tracking images are studied. In view of the drawbacks of the classic Hough Transform algorithm in line detection, an improved algorithm, which can increases detection accuracy and reduce computing time, is developed. Two new corner detection algorithms based on calculating edge curvature are studied. One is based on wavelet transformation and another on polygonal approximation detection. An iterative random Hough transform which can enhance ellipse detection accuracy under strong noise environment is investigated. A new ellipse detection algorithm called curve segmentation detection algorithm is proposed. The algorithm has been proved to be of effectiveness by experimental verification and be able to solve the remained problems which cannot be resolved by classical Hough Transform and Least Square method respectively.(6) The pixel edge detection and sub-pixel edge detection technologies are summarized and two modified sub-pixel edge detection algorithms are proposed. One is based on gauss surface fitting technique, another based on radial basis functions interpolation techniques. Basic principles of the two algorithms can be briefly described as follows. Firstly the Canny operator is used to detect the coarse position of an edge, and then the sub-pixel edge detection of the edge is implemented within the small area of the coarse position. Experimental results show that two algorithms can reach0.1pixels accuracy and0.03pixels resolution separately.(7) A6D measurement experimental setup is built up based on the tracking, positioning and measurement techniques of PTZ cameras. The setup then is used to investigate and verify the ideas and algorithms proposed in the dissertation. The performance of the setup has also been tested. The characteristics and application prospects have been summarized.At the end of the dissertation, the future research topics are briefly introduced.