Automatic Generation of 3D Building Models with Multiple Roofs

Based on building footprints (building polygons) on digital maps, we are proposing the GIS and CG integrated system that automatically generates 3D building models with multiple roofs. Most building polygons’ edges meet at right angles (orthogonal polygon). The integrated system partitions orthogonal building polygons into a set of rectangles and places rectangular roofs and box-shaped building bodies on these rectangles. In order to partition an orthogonal polygon, we proposed a useful polygon expression in deciding from which vertex a dividing line is drawn. In this paper, we propose a new scheme for partitioning building polygons and show the process of creating 3D roof models.

Joint shape and color descriptors for 3D urban model retrieval

With the rapid development of photogrammetry,computer vision and three-dimensional(3D)modeling technologies,it is possible to efficiently construct detailed 3D urban models.Accordingly,large corpora of 3D models,such as the Google 3D Warehouse,are now becoming freely available on the web.How to find the proper 3D urban models is a challenging research issue.In this paper,we join shape descriptors and color descriptors for 3D urban model retrieval.The query objects are localized and segmented automatically from the input images by using a new selective search voting algorithm.Through combining the normalization with the light field descriptor,the Horizontal Light Descriptor is introduced to measure the shape similarity among the normalized urban models.The color descriptors are used to represent the color information of the urban models.The two types of descriptors are joined to search 3D urban models similar to the query objects.Experimental results have shown the effectiveness of our approach.

Mapping the spatio-temporal visibility of global navigation satellites in the urban road areas based on panoramic imagery

The satellite visibility number of GNSS is an important indicator for evaluating its availability for positioning and navigation.In urban areas,urban canyons cause serious satellite signals block,resulting in positioning uncertainty.Many studies used 3D city models to evaluate the visible satellites in some areas at a certain time.Nevertheless,this kind of method is difficult to apply because 3D models are not widely available.This paper thus proposes an easy method to evaluate the visibility of satellites with widely available street view panoramic imagery and GNSS ephemeris.The proposed method utilizes the locations of street view panoramic imagery and the associated GNSS ephemeris to calculate the visible satellite number at different times.Hence,the visible satellite number at a specific time can be mapped.Moreover,the visibility of satellites can be predicted according to its orbit parameters.To evaluate the effectiveness of the proposed method,Wuhan and Shanghai were taken to map post-event,real-time and forecast GNSS visibility.The experiments demonstrated that the proposed method provides a light weighted and easy to use solution to map the spatio-temporal visibility of satellites in urban areas,which is an important reference for GNSS stations layout and positioning qualities evaluation.