WANG Jizhou, LI Chengming
KEYWORDS: 3D; GIS; Modeling
When 2DGIS can not meet all the demands from various urban users, 3DGIS emerges as the times require. For the high complexity in both theory and technology of 3DGIS, the research is still in elementary stage. To develop 3D digital city and make its applications, at first we have to solve the bottle-neck problem that how to build the 3D city model efficiently and quickly. In this paper, we design and implement a method which is composed of four steps including UAV (Unmanned Aerial Vehicle) remote sensing, monoscopic photogrammetry, detailed 3D modeling and 3D visualization.
Firstly, acquiring high resolution images by UAV. As a new platform of Remote Sensing, UAV has many good characteristics such as low cost, simple manipulation, flexibility and etc. To get ideal photos, we manufactured three kinds of UAV£¬installed digital cameras and navigable equipments on it. From tests of UAV images acquired from various shooting conditions, we draw the conclusion that 45¡ã and 300 meter are the ideal shooting angle and height.
Secondly, extracting geometry and texture information from UAV images by monoscopic photogrammetry.
Different from the traditional photogrammetry which needs stereo-mate, we developed a monoscopic photogrammetry method which only uses a single photo. The method is based on collinearity equation. In a single UAV image, we take every buildings as research objects, by dividing the parallel lines on buildings into three groups which parallel X, Y and Z coordinate axis respectively, we compute the photo parameters including the inner elements (x0, y0) and f , the angle elements A,¦Áand¦Ê, and the scale N, and on the basis of all the parameters we can measure the real height of every buildings. We also pick up the texture from the photo and accomplish orthographic rectification.
Thirdly, building 3D digital city. Using all the information we acquired from UAV images, we can reconstruct 3D models of all the objects in city one by one. In order to increase the modeling efficiency, we also established 3D Model Database which has many finished models that can be directly used including street lamp, telephone box, ash bin and etc.
Fourthly, developing 3D visualization software. We implemented a software named NewMap3DV that realizes displaying the 3D scene of a whole city smoothly, which has the data amount beyond 10GB.
Using the above series techniques, we have already built about twenty 3D city models in china.