This research explains vision based semi-automatic construction of 3D-City models from airborne laser scanner (ALS) data. ALS data pre-processing involves noise removal by smoothening, edge-detection and vectorization for urban building boundary edges. Segmentation of ALS data performed to extract roof regions. Both the boundary and roof edges have been vectorised and polygons representing buildings obtained to compose 3D city models. Descriptions on the possible applications of the 3D urban models with special references to Virtual City models and Geographic Information Systems (GIS) have been provided.
About three years ago, airborne laser scanner systems (ALS) started to become available to the mapping and Geographic Information Systems (GIS) industries, and some researchers have started to include the DSMís data in the research and development of automatic building extraction systems     . There are only a few studies solely based on Laser scanner surface data   . Helicopter based systems with higher resolutions of 5 or more measurements per square meter have been reported for 3D building modelling  . Within the automatic systems, aerial images, laser DSM, and 2D plans have been utilized alone or in combination to generate 3D building models. Automatic Systems working solely on the basis of Laser DSMís have been reported . Laser DSMís have the great advantage of representing 3D geometry directly. Also, it is possible to estimate the parameters of planar structures quite accurately with DSM of high resolution.
In the field of GIS not many computer vision oriented techniques have been employed in 3D urban modelling from Laser scanner research. Computer vision techniques such as boundary detection, roof edge detection based on segmentation and plan fitting, thinning, polygonisation and 3D model fitting are new to the GIS Laser Scanner data processing. Therefore these methods can be considered as new efforts for 3D building modelling. The present research methods extract edges, segment data into regions related to man-made buildings from laser radar images (Fig. 1). The segmentation results and edges are to be processed by fitting models to the data. Fitted models are to be used to build a photo-realistic model of the scene to be displayed for the purpose of scene characterization.
Fig. 1: Flow chart of vision based complex roof detection from ALS and 3D building modelling