Parametric Comprehensive Simplification Of 3D City Model Based On PCA And CSG

With the continuous development of the information age and digital city(smart city),mobile phones,tablet PCs and other mobile devices continue to spread,electronic maps,mobile navigation is more and more widely used.With the increasing accuracy of the collected data,the volume of 3D city model data is getting bigger and bigger.Due to the limitation of network bandwidth and hardware condition,the traditional visualization of the 3D city model has been difficult to be realized on the mobile terminal,which needs to simplify the 3D city model urgently.We should reduce the amount of data as much as we can while ensure the accuracy and completeness of the model information.Parametric technology is a computer-aided design technique,it maintains the association between parameters(also known as variable)and the geometry objects.We can control the characteristics of the geometry objects by adjusting the parameter values.In this paper,we propose a new idea of taking CSG voxels as parameters to simplify the 3D model and reduce the complexity of visualization.Principal Component Analysis(PCA),which can analyze the main influencing factors from multiple objects,it reveals the nature of things and simplifies complex problems.PCA can also be applied to 3D city model data.In this paper,the PCA method is used to reduce the dimension of the 3D data,the polygons of the 3D model are merged,and the polygons could be reduced,then the LOD3 models are transferred to LOD3 ES models,so we can get ready to the next step to simplify.Constructive Solid Geometry(CSG)is also called voxel construction.It constructs spatial entities by basic voxels with the operation such as geometric transformations,Boolean operations and local modifications.It can also be applied to the simplification of 3D city model.In this paper,we propose a new structure City Tree.And the LOD3 ES model(model simplified by PCA)is simplified with it.Then the 3D city model is segmented,prototypes are extracted,then the model is rebuild.According to the experimental results,the 3D city model can be visualized with multi-level precision,and the maximum amount of data compression can be achieved without information loss.It is more convenient and efficient in the practical application.