基于纹理数据和SCSG-BR表示的城市建筑物混合 建模

随着城市建设的迅猛发展,城市建筑物建模的复杂性和实景化要求越来越高。因此,进行高精度的城市建筑物建模,建立有效的数据结构成为一项具有挑战性的工作。针对结构实体几何（Constructive Solid Geometry, CSG）模型建模的局限性,本文提出了一种结合CSG和BR（Boundary Representation）的混合建模方法。该方法改进传统的CSG为“空间CSG（SCSG）”,利用维度扩展的九交模型（DE-9IM）表示体元间的拓扑关系,确定唯一的SCSG树来表示城市建筑物的外部结构,同时用BR表示城市建筑物几何要素间的拓扑关系。然后,本文结合文件数据库和关系数据库来联合管理模型数据。关系数据库存储模型和纹理的属性信息;文件数据库存储模型和纹理图像。在存储和调用纹理影像时,关系数据库中的面ID将城市建筑模型ID和纹理ID关联,纹理图像和城市建筑模型同时被加载和存储。另外,本文采用最小二乘法对建筑物多边形进行正交化和拓扑调整处理,以保证模型数据的精确性。本文选择美国科罗拉多州丹佛地区和瑞士苏黎世地区的数据进行实验,并根据不同的建模方法进行模型加载耗时的比较,证明本文提出的方法耗时较少。实验结果表明,该混合建模方法不仅可以有效地表示实体的拓扑关系,还可以加快纹理加载,实现建筑物的快速精确建模,有效实现空间查询。

Hybrid Modeling for Urban Buildings Based on Textures and SCSG-BRs Representation

With the complexity of and the photorealistic requirement for urban buildings in rapid development of urbanization, the high accuracy of modeling for 3D urban buildings and the establishment of an effective data structure for those complicated building becomes a challenging work. With consideration of the shortage of the current CSG (Constructive Solid Geometry) modeling, this paper presents a hybrid modeling, which combines CSG and BR (Boundary Representation). In the proposed model, the traditional CSG model is improved by what is known as "Spatial CSG (SCSG)", which uses the dimensionally extended Nine-Intersection model (DE-9IM) to represent the topological relations between voxels and determines the unique SCSG tree to represent the exterior shape of the buildings. And then, the BR is used to represent the topological relationship between geometric elements of the urban buildings, which considers the texture as the attribute data of the wall and the top and combines SCSG as SCSG-BR method. This proposed method combines the file database and the relational database to manage the data of three-dimensional (3D) buildings. The attribute information of the building model and the texture are stored in the relational database. The file database contains a model file and a texture image file, which are used to store the building and the texture image. The texture images are separately stored in another relational database by a variable-length binary data type. During the storage and recall of texture images, the urban building model ID and the texture ID are linked through face ID in relational database. The texture images and the urban building model are loaded and stored at the same time. Thus, the management method has less complex processes in texture mapping and improves the model loading speed. In the data processing, the least squares algorithm is used to normalize the building polygons, and adjust the polygon topology to ensure the accuracy of the modeled data. Data sets, located in Denver, Colorado, USA, and Zurich, Switzerland, are selected to validate our method. The time-consuming comparison of model loading using the different modeling methods are conducted, and the experimental results demonstrated that our method consumes least time out of all methods. The experimental results also demonstrated that the hybrid modeling method proposed in this paper can not only accurately represent the topological relations of the building entities, but also quickly load the building texture images, which is capable to achieve fast and accurate modeling buildings, and effectively realize spatial query.