The Research On Rapidly Realizing 3D Visualization For The Main Body Of Street Sight In Cyber City

As we know, there is no accurate definition widely accepted for cyber city till now, just as that of digital earth. Actually, cyber city is the counterpart of real city in virtuality, an informationized city. it is a system combined the techniques of RS, GIS, GPS, internet, virtual reality etc., to implement the automatic collection, dynamic monitoring and management, assistant decision-making etc. for the infrastructure and functional mechanism of city. The establishment of 3-Dimensional City Model (3DCM) is the fundmental process for the realization of cyber city. As the real 3D sight of city is more and more indispensable in urban planning, the design of architecture sight, 3D navigation, the textured 3DCM is showing good application and economic benefit for the future .Since the street is a primary component of city, it is very significant for 3DCM that how to rapidly realize the 3D visualization of street sight. The sight of street consists of two parts: one is main body, including facades along the street and the road etc.; the other is detail sight, including pedestrian bridges, line trees, parterres, signposts and street lamps etc. In general sense, the facade is the outer wall of building. In 3DCM, texture of terrain and the roof of buildings is acquired from aerial images. The textures of building facades, however, are still acquired from images taken manually with digital camera. Since lacking index of images, the processes of searching images, preprocessing images and corresponding images with buildings are implemented manually. As a result, the problems of low efficiency and high labour intensity emerge. Therefore, it is a problem urgently needed to be solved that how to rapidly and really reconstruct the facade along the street. The 3D reconstruction of the road and detail sight is also a hot issue in cyber city. The acquisition of vehicle-based image sequence for buildings has the characteristics of convenience and rapidness. The resolution of textures obtained from vehicle-based sequence is furthermore higher than those obtained from helicopter-based image sequence. Therefore, it will be aided greatly by the automatic processing of textures from vehicle-based image sequence that the 3D visualization of street sight in 3DCM.The research involved in this paper consists of two aspects: (1) the rapid reconstruction of facade along the street based on side-shooting vehicle-based image sequence, including the preprocessing of image sequence, the recovery of the building texture and the 3D reconstruction of facade along the street; (2) image sequence along the optical axis can be employed to reconstruct the road and detail sight of street, therefore, pilot study is implemented on the photogrammetric issues involved in the processing of image sequence along the optical axis including parallax, relative orientation, forward intersection, resection etc.. The purpose of this research is to provide a scheme, which is a breakthrough for the thought of traditional close-ranged photogrammetry, for the reconstruction of facade along the street based on the combination of the theories and methods of photogrammetry, computer vision and image processing; the research on the photogrammetric issues is the extension of traditional photogrammetry , in the instance of the stereopair along the optical axis, based on the existing geometric theory of stereopair and the theory of optical projection. (1) The rapid reconstruction of facade along the streetIt is necessary to implement the preprocessing of image sequence before the recovery of the facade texture. Because the number of image sequence is always very large, it will be time-comsuming and labour-comsuming that the processing of all of the images. Furthermore, the overlapping rate is always over 95% which is unnecessary since the overlapping rate of60% is enough for the recovery of facade texture. As a result, the process of automatically selecting images should be implemented, based on the proportion of building texture in the image and the overlapping rate of image sequence, to reduce the redundance of image sequence; As we know, close-ranged DC images are greatly affected by lens distortion. The straight lines in the images got curved by the influence of lens distortion. Therefore, the influence should be eliminated, an algorithm is presented to calibrate the lens distortion according to the curvature of straight lines caused by it; Since the occlusion of trees goes against the extraction of lines from buildings, the occlusion area should be automatically distinguished and removed. An algorithm of occlusion removal employed information of hue and lines is introduced. Since the oblique angle of close-ranged DC images is large, there is obvious geometric distortion of fac,ade texture in the image. Therefore, the process of rectification of raw image is necessary to acquire the texture similar to real facade. An algorithm is presented to determine the DC parameters employed the constraint of straight lines bundle and the constraint of known orientation of parallel lines in object space.? The recovery of facade texture. To calculate the projective difference of corresponding points on the same projective plane acoording to the DC parameters determined. Then automatically detect the depth change of facade texture in the image by the histogram of projective difference of corresponding points created so that the image sequence can be subsected automatically; It is deduced to determine the relatively spatial relationship of the images facade texture involved that a model of least square adjustment, similar to the strip block adjustment, based on the formula of the projection of image point on the projective plane with the DC angular parameters determined early as weighted observation. Then a method similar to that of generating ortho-image is employed to generate the whole facade texture.? The correspondence between facade texture and 2D vector map. After the subsection of image sequence and the rectification and mosaic of facade texture, several ground control point(GCP) is measured manually on the 2D vector map to correspond the facade texture with the contour line of buildings along the street so that the facade along the street is reconstructed.(2) The research on the photogrammetric issues of stereopair along the optical axis? The concept of radial parallax and tangential parallax is presented to replace the traditional horizontal parallax and vertical parallax; The formula of relative orientation of stereopairs along the optical axis is deduced according to the formula of displacement caused by small angle;? The formula of forward intersection along the optical axis is deduced based on the constraint that the distance between the projective points of corresponding points should be minimum;? Resection of vehicle-based imagery based on the vanishing point geometry. The initial value of DC parameters is determined by vanishing point geometry, the GCPs are acquired via the point match between vehicle-based images and ortho-images combined with the LJDAR data;? The recovery of road texture based on image sequence shot along the optical axis.