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ABSTRACT:Over the past ten years technologies for generating, maintaining and using 3D geo-information have matured. For national mapping agencies one of the challenges is how to best extend 2D data into 3D data, making best use of research results and available technologies. Some mapping organisations are making serious progress. The question addressed in this paper is how research results achieved in the past ten years are applied in practice and what research problems remain. In addition, the paper explores the potentials of the OGC 3D standard (i.e. CityGML) for 3D national mapping and what developments are further required to make the standard better fit for this purpose. The main conclusions of the paper are that 3D data is more and more available but still suffers from a low level of usage (mainly visualisation) and standards and formats based on CityGML have been stabilised although software support is still in the early stage. Several recommendations are made to meet these problems, including the definition of European CityGML profiles (as the INSPIRE Building profile) to harmonise 3D needs and standardise 3D implementations at international level.

Abstract. Data and models of the built environment enable urban systems to serve their inhabitants and adapt to ever increasing rates of change in society, climate, and. Models of the built environment at or above the ground surface need to be 3 dimensional to best fill that role, but the subsurface also has critical 3-dimensional properties that are even more difficult to characterize being hidden from view. There are many compelling use cases for high quality data on the underground environment at varying levels of detail, from which a list of 6 critical use cases are presented here. Data on the location and disposition of buried utility are difficult to collect and maintain, but the value of avoiding damage, delay, injury and cost with good underground data in all these cases far outstrips the cost and difficult of obtaining it. Effective management and utilization of underground data also depend on models and schemas to organize them. Sharing and exchange of such data require standard models that are agreed between data providers and consumers. There are presently a number of applicable models and standards, but they often reflect a specific perspective, focus, and priorities that make it difficult for any one of them to provide a holistic awareness of the entire underground built environment at the multiple levels of complexity required by the use cases. The draft Model for Underground Data Definition and Integration (MUDDI), a comprehensive integration model for underground information takes a modular approach, with a conceptual core that covers basic geometric representations of underground assets, and a number of extension modules that add more specialized capabilities as well as interfaces with existing models. Several prototyping efforts have generated physical implementations of the MUDDI conceptual model and application deployments populated by operational utilities data, in particular the NUAR and LUAR pilot projects sponsored by the UK Geospatial Commission. An Open Geospatial Consortium Standards Working Group (SWG) is being formed to build on the draft MUDDI model as well as the experiences gained in pilot projects, in order to publish a full specification of the model at the conceptual, logical, and physical levels. Another SWG objective will be to create a roadmap of critical extension modules, particularly those which support upcoming 3D-4D digital twin technologies for visualization, operation, and simulation. Other advanced use cases for these extensions, such as mixed reality visualization and navigation, are expected to become common as both the demands on our built environment and the data available to manage it continue to expand.

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