EN/CityGML-Tutorial/chapter-2:-Building/LOD2.md

@@ -6,7 +6,7 @@ In LOD2, the shape of roof can be modeled in addition to LOD1. Additionally, sta
 
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-For the geometries of a LOD2 building, the CityGML 2.0 standard allows the use of MultiSurface elements. However, a MultiSurface geometry does not guarantee the necessary topological connection of its surfaces. Based on use case, it is recommended to model BoundarySurfaces as MultiSurface (e.g. for visualization purpose) and a building with solid geometry (e.g. for building energy demand simulation). The [CityGML standard](https://portal.opengeospatial.org/files/?artifact_id=47842) conformance 10.3.9.4, page 78, requires that a solid geometry starting from LOD2 must be inserted using references to the polygons of their respective boundary surfaces. These references have to be made using xlink concept of GML 3.1.1. More information on correctly inserting solid geometries to CityGML building object can be found [here](https://gitlab.com/volkercoors/CiD4Sim/-/wikis/usefulTools/FME-Workbenches-(EN)).
+For the geometries of a LOD2 (also LOD3 and 4) building, the CityGML 2.0 standard allows the use of MultiSurface elements. However, a MultiSurface geometry does not guarantee the necessary topological connection of its surfaces. Based on use case, it is recommended to model BoundarySurfaces as MultiSurface (e.g. for visualization purpose) and a building with solid geometry (e.g. for building energy demand simulation). The [CityGML standard](https://portal.opengeospatial.org/files/?artifact_id=47842) conformance 10.3.9.4, page 78, requires that a solid geometry starting from LOD2 to inserted using references to the polygons of their respective boundary surfaces. These references have to be made using xlink concept of GML 3.1.1. The below figure shows a LOD2 building with solid geometry containing external references (xlinks) to its BoundarySurfaces.  More information on correctly inserting solid geometries to CityGML building object can be found [here](https://gitlab.com/volkercoors/CiD4Sim/-/wikis/usefulTools/FME-Workbenches-(EN)).
 
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@@ -14,6 +14,14 @@ For the geometries of a LOD2 building, the CityGML 2.0 standard allows the use o
 
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+**An example LOD2 building with Solid Geometry**[^1]
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+</div>
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+[^1]: [SIG3D Modeling Guide for 3D Objects - Part 2: Modeling of Buildings (LoD1, LoD2, LoD3)](https://en.wiki.quality.sig3d.org/index.php?title=Modeling_Guide_for_3D_Objects_-_Part_2:_Modeling_of_Buildings_(LoD1,_LoD2,_LoD3)#Building_.28bldg:Building.29)
+
 An XML document of a CityGML 2.0 LOD2 building object with building solid geometry will look like this:
 
 ```plaintext