Digital Image Based Camero Calibration With Twice Steps Method And Inaccuracy Analysis

In the field of geological exploration, water conservancy construction, mine exploitation, city planning and large scale equipment manufacturing, it always need to survey some thing in the long distance or in the vile environment. Location is the first step of the survey. Now there are several ways to location such as satellite positioning, laser ranging, water level equipment and based the digital image ways to survey. Satellite positioning has got a relatively high precision. The speed of survey is fast while the cost of the whole system is expensive and it need signal launch equipment. Laser ranging system has millimeter-level accuracy. But it has blind area of survey and it need target reflector when it is working. Water level equipment is simple while the efficiency of survey is low and the operation is complex.With the development of the computer and digital image technology,using common camero to survey has became ture. The first step of survey with digital image is calibration and solving the parameters of the camero .There are mainly two kinds ways of calibration. They are standard reference substance based calibration and self-calibration.The calibration based standard reference substance is mainly represented by points based camero calibration. Self-Calibration methods contain self-calibration of rotating, self-calibration with vanish points and self-calibration with parallel movement. Standard reference substance based calibration void to solve the nonlinearity mathematical equations,but it must set the reference substance and accurately have the positions of the points in the frame of axes of the world. Self-Calibration of rotating and with vanish points ways need some points on the surface of the measured object but the positions of them need not to know.It is hard to carry out the working with this calibration method when there are little points existing on the measured object. Self-Calibration with parallel movement need camero can move in many directions and it makes the structure of the system complex.The paper combine the merits of the standard reference substance based calibration and self-calibration to raise a new way of calibration after comparing and analysising the principles of them.The new way use two steps to calibrate the camero and survey.First, set the standard reference substance in the relatively short distance and use points based calibration to solve the parts of the parameters of the camero.Then adjust the focus and make the measured object in the long distance form a clear image on the screen.In this position, sample the image and Move the camero once,in the new position do it again.Get the final measuring result through getting the positions of the characteristic point on both images and solving the equations using these datas.Use the software called matlab to analysis the precision of the new calibration method. Quantitatively analysis the affects between some factors and the final measuring result.These factors are the precision of the calibration,the parameters of the camero,the precision of the distance of moving,the precision of the positions on the image and the length of the movement distance.This paper gives an example of the precision analysis and a simple model of the system.The new method of calibration with twice steps voids the shortcomings of the satellite positioning, laser ranging, water level equipment in the long distance and large-scale things' survey. Comparing with the ordinary ways of survey with digital image,this new method need not set the standard reference substance in a long distance and there are no specific requirements on the measured objects.These features simple the system and operation.It has significant value in the theory and practice.