Modeling of urban planning actions by complex transactions on semantic 3D city models

Decision support for environmental planning requires the impact analysis of envisaged actions. These actions often are adapted from measures specified in regulations or other legal documents given in natural language. Their realization involves (possibly complex) changes to specific parts of the environment. For example, the energetic retrofitting of a building typically comprises the insulation of the façade and replacement of the windows. In general, different actions or combinations of actions can be chosen for the optimization of certain key performance indicators (KPI) like the overall energy demand or CO₂ emission of a city district. This requires the assessment of the applicability of the possible actions to the individual elements of the environment, their potential interferences, and their effects on the KPIs of interest. The paper presents an ontology for the formal modeling of planning actions as complex transactions on the entities of virtual 3D city models using UML. This comprises the representation of the required transactions on the underlying objects of the city model, the preconditions for the applicability of the action, the required actual resources like duration and costs if the actions would be performed in the real world. Also the affected KPIs like 'CO₂ emission' or 'en-ergy demand' are enumerated together with qualitative indicators stating whether the action will have a positive, a negative, or no effect on them. The model builds upon the international standard CityGML of the Open Geospatial Consortium for the representation of semantic 3D city models which is used worldwide by an increasing number of cities, regions, and even entire countries. The proposed model allows to map the measures and actions described in legal documents and regulations (e.g. energy savings regulations) onto complex transactions on objects from virtual reality. This enables planners to work with high level transactions directly corresponding to measures and actions as described by legal frameworks instead of individually manipulating the many objects, attributes, and relationships within a geoinformation system required to simulate the outcome of a complex real world action. We illustrate the concept for the use case of strategic energy planning in an urban quarter in London where decisions on the sensible degree of retrofitting of individual buildings in an socially disadvantaged district have to be made.