Research On3D-Openness In Urban Area Based On Urban Digital Elevation Model

The form of urban open-space is closely related to the city physical environment and the city view environment. The Openness has been commonly used to describe the shadow impaction of visualization or sunshine from neighborhood buildings or terrains in urban area. The original openness model has some restraints such as the view angle is confined to a certain scope or the space under the viewpoint is ignored. The openness of urban open-space in various forms are difficult to get a detail description by the original model. Hence, we developed the new model based on the original one, which overcomes the limitation and aims to perfect the theory of openness. The new model could be used in urban landscape design and city planning.Primary works and contributions of this thesis are summarized as follows:1. Concept of3D-Openness model is given. Analysis of the limitation of the original model, a3D-Openness model is developed. The view sphere is used for measuring visible urban space quantitatively. The space all in the sphere including which is under the viewpoint is take account of the calculation of the openness for a given location. in a way that is different from its predecessors. The conception of3D-openness and model elements that contain viewpoint, barrier and maximum visible distance, are elaborated on in the paper. The new model is suitable for the city with high-density building.On the basis of visible space characteristics, quantified parameters about the hierarchy, the fluctuation, the direction about the visible space are constructed.(1) Among these parameters, the Quantity of Levels and Height Width Ratio(HWRatio) are about visible space hierarchy.(2) Wave Frequency and Wave Range parameters are about visible space fluctuation, whose calculation methods based on the city skyline. Wave Frequency is defined for measuring the times of the visible space in one direction different from the next direction. Wave Range is defined for measuring the difference between the visible space in two direction.(3) Shape Index, Skewness, Connectivity and Open Direction parameters are about visible space direction, whose calculation methods based on the2D graphics which are derived from the3D visible space projection. Shape Index is defined for measuring the complexity of visible space. Skewness is defined for measuring the even degree of visible space. Connectivity is used to describe the patency in one direction and the direction with highest patency is Open Direction.(4) Visible Ratio is defined as the3D visible volume divided by the volume of view sphere, which is used for measuring the percentage of the visible space that is filled up by the hypothetical spherical view area.2. Automatic extraction of obstacles in all directions and quantified parameters are carried out with Urban Digital Elevation. The elements of3D-Openness model suitable for Nanjing Old City are chose by researching. Based on the simulated data, the automatic extract results are verified and the accuracy and validity are analyzed and discussed.3.The empirical study in Nanjing Old City on3D-Openness model is carried out. The viewpoints in the area of various use types are analyzed and discussed. The3D-openness of main road is also extracted and analyzed. A typical block of3D-openness parameters are discussed in different ways.The improved openness model has overcome the limitations of the original one and it can describe the open-space in different analysis angles. The new3D-openness model have actual application value in the selection of sites and the design of houses.