Bidirectional enrichment of CityGML and Multi-View Stereo Mesh models

Abstract

The use of 3D city models has increased the last decades due to the evolution of technology. Their use is related to the need for solutions on issues that correspond to the building environment. Modelling aspects, like geometric, semantic information and topology are necessary, in order to provide an integrated result of spatial analysis. The creation of a complete 3D city model that contains all the needed information for an application, is a time consuming and complex process. Furthermore, different 3D city model formats can contain different aspects of the same features. For example, a CityGML model can have the semantic information of a 3D object, while a Multi-View Stereo Mesh model can contain all the geometric and appearance information of the same 3D object.
This thesis is documenting the possible enrichments that can be done bidirectionally between these two different 3D city model formats, when both exist for the same entities. Moreover, it presents the exploration of possible automated enrichment methodologies that can enrich each 3D city model automatically with information from the other one. Finally, an automatic bidirectional enrichment methodology is proposed and is implemented on a testing area, provided in the two different 3D city model formats. This method is based on distance computations between the meshes of the two 3D city models, used to match corresponding features, or part of features, in order to segment semantically the Multi-View Stereo Mesh model (roof, wall, road, terrain, uncertain) and transfer texture to the surfaces of the CityGML model that correspond with the surfaces of the Multi-View Stereo Mesh model.
In addition, distance computations are performed for the validation of the absence of buildings and the shapes of the roofs in the CityGML model, with respect to the information given from the Multi-View Stereo Mesh model. After the implementation of the proposed methodology, it is found that both 3D city model formats can be used for the proposed enrichments of either 3D city model format.
Future improvements are presented for the achievement of using existing information of different formats of 3D city models of the same entities, in order to supplement each 3D city model format with useful information, enhance the performance of spatial analysis and boost the evolution on the use of such models on real life applications.