A Study On Building Extraction And Three-dimensional Landscape Reconstruction In Digital City

With the rapid development in GIS, the representation and processing of three-dimensional information become greatly in demand. A three-dimensional city model with the ability of management and manipulation should be established in order to manage and organize 3d data in large quantity. This thesis explores to validate building extraction from altitude data, the representation of building models and the reconstruction of 3d city landscape.Firstly, the theories of range image segmentation are applied to automatic building extraction from digital elevation models. The information about the buildings is contained in the difference between original DEM and an approximation of topographic surface without buildings. Therefore we use mathematical grey scale morphology to realize the background estimation and elimination. The threshold for segmentation can be dynamic motivated by altitude information of terrain surface and derived from prior knowledge about the buildings. A building is defined as a set of planar patches in the same 3d region, which enables us to define criteria for buildings from our 3d data. Building and vegetation classification relies on the study of distribution of the normal to 3d local surface.Two edge operators are used to track the border of feature areas. The relationships of feature borders are represented by a tree structure. Freeman chain codes and a merging algorithm are applied in order to convert feature areas from raster to vector.Secondly, methods of data modeling based on geometry primitives, blocks and topology are analyzed. According to building structures and geometry constraints, several typical simple building parametric models are given.Finally, a city landscape is built up based on DEM and aerial imagery. On the basis of building extraction, 3d city landscape can be built up by reconstructing buildings and terrain separately. But this also brings the matching problem of buildings and terrain, which should be resolved by model transform. The general rendering method in digital elevation model including building altitude information brings the problems of sloping building walls and the mixture of buildings and terrain. An approach of extracting buildings from digital elevation model data by utilizing the great altitude difference between building vertices and terrain vertices, and the geometry characteristics of buildings is developed.