EN/CityGML-Tutorial/chapter-2:-Building/LOD3.md

 In LOD3, the shapes of openings such as doors, windows can be modeled in addition to LOD2. BoundarySurfaces (e.g. WallSurface, GroundSurface, RoofSurface, ClosureSurface) are modeled using CityGML property of "boundedBy" while openings (e.g. Door, Window) can be modeled using CityGML property of "opening". BuildingInstallation objects can be optionally added with CityGML property of "outerBuildingInstallation". LOD3 buildings and scenes are used more in small-scale
 analyzes or in visualizations for urban planning, for example in the context of citizen participation.
-Publicly available 3D models in LOD3 are therefore also rare.
+Publicly available 3D models in LOD3 are therefore also rare.  A simplified UML diagram of CityGML 2.0 LOD3 building object is shown below:
 
 **LOD3 daata model**