LEVEL OF DETAIL IN 3D CITY MODEL
3D city models are derived in different levels of detail (LODs), based on the acquisition technique and intended application of the data. CityGML supports storing multiple representations, and it differentiates them by defining five LODs depending on the geometric and semantic complexity of the model.
For buildings, the following LODs are described-
LOD0 models present the transition from 2D to 3D GIS without volumetric features. These models are the footprint containing the elevation and a polygon representing the roof edges.
LOD1 is a block model that is usually derived by extruding a footprint to a uniform height. They are also acquired automatically with a number of different techniques, such as using existing data in cadastral databases or analyzing point clouds derived from airborne laser scanning. These models are used for a wide range of applications like computational fluid dynamics.
LOD2 mandates a generalized roof shape and larger roof superstructures. They are either derived automatically or obtained with photogrammetric techniques. LOD2 models are useful for rooftop solar potential estimations.
LOD3 is a detailed architectural model containing roof overhangs, openings, and other facade details. Models at LOD3 are obtained with a conversion from BIM models or from terrestrial laser scanning. The presence of windows and other details makes them useful in applications like energy simulations.
The LOD taxonomy of CityGML is completed by LOD4, which is an LOD3 containing indoor features like rooms and furniture. These models mark the boundary of GIS and BIM. Datasets modeled at LOD4 are useful for spatial analyses that integrate both outdoor and indoor features like simulating floods for predicting damage of buildings and navigation.
While many spatial analyses are possible with any of these LODs, data in finer LODs usually comes at a higher accuracy and it brings more reliable results in a spatial analysis.