Research Of Monocular Vision Coordinate Measurement System Modeling

With the rapid development of science and technology,the appearance design of large and giant product in Aviation, aerospace, military and civilian areas are more and more complex. And its processing and assembling have become increasingly demanding high precision and in most cases real-time requirements of the scene. So the traditional Measurement of the content and methods have been unable to meet the three-dimensional space measurement requirements of the modern production. There is an urgent need to find a ladge-size three-dimensional overall field test technology and system which can carry out three-dimensional high-precision structure measurement to large pieces of weapons and equipment in the scene of production, assemble and use, such as missiles, satellites, aircraft, tanks and so on. While Vision coordinate measurement technology is a new three-dimensional space coordinate technology based on computer vision and coordinate measuring technology research, which has adopt to higher demand of the measuring technology of the modern product in aspects of measuring accuracy, measuring range from a new thinking of coordinate measurement.Basing on vision coordinate measurement technology, this thesis poses monocular vision coordinate measurement system on the base of measurement probe imaging.This method has changed the previous condition that vision coordinate measurement instrument is limited by acquiring and processing the measured appearance directly, and also changed the condition of limit application because of complex shape of measured object. So it is fit for online measurement of industrial site. For the whole vision measurement system, the primary task is to set up the system modle, which is also the key influencing factor to measurement system precision. Here,we focus on sovling the problem of system modleing of monocular vision coordinate measurement.The system is maily composed of high Resolution black and white CCD camera, a lens with infrared high-pass filter, a portable industrial computer, image acquisition and processing system, a RS-485 serial communication interface and so on. Through the 5 analysis of optical characteristic points'imaging coordinate on optical measurement probe, making use of knowledge of geometric constraint among every characteristic point we know, and linear calibration of camera nonlinear modle, we can fix the characteristic points'relative coordinates to camera coordinate system, and fix the measured points'space coordinates by making use of the position relation between probe tip(contact) and the characteristic points, then realize all functions of coordinate measurement instrument.This thesis set up the system model through perspective projection camera model corrected by making use of two-dimensional distortion image, image coordinates with optical characteristics and measurement principle of optical probe's geometric location constraint knowledge. Also it gives out the specific solution process, and fix the space coordinates of measured points(probe tip) based on pose optimization algorithm of space coordinate constraint. In order to make the model practicle, we need to increase the system model's precision and stability. So we pose all kinds of factors which could influence precision and stability of the system model, and give out the specific solution. Then we introduce imaging model of camera, realize that the camera is a nonlinear model with distortion during actual imaging process. In order to solve the problem of that, and make the image point more close to ideal image point of camera linear model, also decrease the error of system, increase demarcate precision, through the analysis of the fomer nonlinear distortion correction method, only considering radial distortion of lens, we pose nonlinear distortion correction method based on cross-ratio invariance, which is a demarcate method independent to other internal and external prarmeters, with simple calculation, fast and accurate. And because of instability factor existing during the process of probe tip pre-calibration and replacing, we must calibrate the probe tip coordinates accurately before erery measurement in order to make its influence to the system model decrease to least. Thus, we adopt the constraints of camera's coordinates no changing during the swing process for the probe tip fixed in spherical seat to correct the probe tip's coordinates. Then, for the characteristic of optical characteristics point in probe tip, we do the research of centroid position to the image point of characteristics point. Considering the Gauss fitting's better anti-noise ability and higher precision compared to centroid method, we adpot Gauss Bi-cubic interpolation algorithm to solve the centroid position problem in monocular vision coordinate measurement system. But it has only made use of imaging edge points of characteristics points, ignoring the other points'function on the whole characteristics points imaging surface. So, basing on traditional Gauss fitting algorithm, we adpot interpolation algorithm to increase the amount of effective pixels points around the characteristics points, and improve the location precision of characteristics points'center through least square method to eliminate error factors. Thereinto, bicubic interpolation has increased 16 effective pixels around characteristics points, more than bilinear interpolation, and it could improve the precision. Finally, it makes verified test of system parameter correction, centroid location and system measurement model by making use of self-made plane target and Matlab program, and also analyses the error factors causing precision and stability of system model. Under the actual experiment condition, the experiment indicates that the system model set up by this thesis only could be used in site measurement with not high precision demand.