Automatic Semantic-preserving Conversion Between OBJ and CityGML

We investigate the automatic conversion between two substantially different formats used in 3D city models: the ubiquitous but semantically poor Wavefront OBJ and the semantically rich but less used OGC standard CityGML. We elaborate on their differences and on the challenges involved in their conversion, such as the inference of semantics in an OBJ file for their use in CityGML, and the storage of these semantics back in OBJ. We implement two software prototypes: a conversion of 3D building models from CityGML to OBJ (CityGML2OBJs), and one from OBJ to CityGML (OBJ2CityGML). By presenting both methods and implementations, we aim at increasing the availability of CityGML datasets and the possibility to create them in powerful 3D modelling software.