Input data requirements for daylight simulations in urban densifications

Abstract

One of the biggest challenges in urban densifications is securing adequate daylight access. This study examines the potential of using semantic 3D city models as input to daylight simulations. It is focusing on investigating input data requirements to these simulations from a geodata, 3D city model specification and measuring guideline perspective. To achieve this, geodata simulation input requirements for the most common daylight metrics are documented. Next, 3D city model data from two Swedish municipalities along with 3D data constructed by ourselves in CAD- and GIS-environments are utilized to explore the impact of using 3D city models of different levels of detail (LOD) and positional accuracy in daylight simulations linked to Swedish and European laws and recommendations. Similarly, the measuring guidelines and 3D city model specification requirements related to balconies and other façade accessories are also evaluated along with the utilization of façade reflectance properties and colour. It is found that LOD1 is sufficient for the obstruction angle metric for most roof types but for e.g., gabled roofs LOD2 should be used. A positional accuracy on a decimetre-level is accurate enough for the aforementioned metric. Daylight factor simulations require that balconies and façade accessories protruding more than a couple of decimetres must be represented in the 3D city model along with information on façade material and colour. The outcome of the study is expressed in the form of a list of recommendations for the creation of national profiles of 3D city models supporting daylight simulations.