Generalization of buildings within the framework of CityGML

For a better visual impression,3D information systems and architecture need detailed,photo-realistic visualization of 3D data-sets.However,easy accessibility with efficient rendering becomes difficult due to the detailed data associated with 3D objects.Therefore,different applications demand different levels of detail(LoD).Currently,City Geography Markup Language(CityGML),as the Open Geospatial Consortium standard,is being used to model and represent buildings in different LoDs(LoD0–LoD4),but it does not provide methods to generate different LoDs automatically.Thus,generalized(abstracted)3D scenes of buildings need to be generated to fulfill the demands of task-specific applications by reducing data volume.This paper discusses various ways to generalize building models,within the framework of CityGML,reducing the level of detail from higher LoD to lower.The LoD4 data is parsed and analyzed.Various heuristics are applied to simplify the ground plan and the results are then aggregated.The minimum length of an edge for simplification is restricted to the CityGML generalization specifications provided and is characterized by differing accuracies and minimal dimensions of objects for LoD1 and LoD2.This could maintain the accuracy of generalized objects and avoid the elimination or merging of important features.Second,the heights of the walls of the simplified ground plans are raised with the aim to construct simplified 3D building models.Algorithms for simplification and aggregation aiming to derive LoD2 and LoD1 are implemented and tested on a number of buildings of Putrajaya,Malaysia.The experiment results show that the minimum length of edges to be simplified is inversely proportional to the size of generalized models.

Integration of CityGML and Oracle Spatial for implementing 3D network analysis solutionsand routing simulation within 3D-GIS environment

3D navigation within a 3D-GIS environment is increasingly getting more popular and spreading to various fields.In thelast decade,especially after the 9/11 disaster,evacuating the complex and tall buildings of today in case of emergencyhas been an important research area for scientists.Most of the current navigation systems are still in the 2D environmentand that is insufficient to visualize 3D objects and to obtain satisfactory solutions for the 3D environment.Therefore,there is currently still a lack of implementation of 3D network analysis and navigation for indoor spaces in respect toevacuation.The objective of this paper is to investigate and implement 3D visualization and navigation techniques andsolutions for indoor spaces within 3D-GIS.For realizing this,we have proposed a GIS implementation that is capable ofcarrying out 3D visualization of a building model stored in the CityGML format and perform analysis on a networkmodel stored in Oracle Spatial.The proposed GUI also provides routing simulation on the calculated shortest paths withvoice commands and visual instructions.