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

@@ -26,7 +26,7 @@ LOD1 and LOD2 are the most common level of details produced by users globally an
 
 # **CityGML 2.0 Building Data Model**
 
-The CityGML building data model (shown below as a UML diagram) defines the geometric and semantic properties to represent a building object in its different LODs. A building object is either a building (Building) or a building part
+The CityGML building data model (simplified excerpt shown below as a UML diagram) defines the geometric and semantic properties to represent a building object in its different LODs. A building object is either a building (Building) or a building part
 (BuildingPart). A building can consist of any number of building parts; these in turn can contain other building parts. In principle, a building object in CityGML can be broken down into many hierarchically linked building parts representing real world building construction.  The common properties of both Building and BuildPart classes are gathered in the AbstractBuilding superclass, which can be modeled with MultiSurface or a Solid geometry. The semantic properties for a BoundarySurface modeled with a MultiSurface geometry are defined beginning from LOD2. For example, semantic properties of RoofSurface, WallSurface, GroundSurface, and ClosureSurface are added in LoD2. From LOD3, in addition to LoD2 the wall and roof surfaces can also have semantic properties of door and window openings. For LOD4, in addition to LOD3 the semantic properties of a Room bounded by FloorSurface, CeilingSurface, InteriorWallSurface can also be added. 
 
 The CityGML standard also defines attributes for every CityObject. The standard defines two types of attributes: Schema attributes and generic attributes. Schema attributes are part of the data model for each thematic module. The CityGML building data model defines schema attributes such as building class, function, yearOfConstruction, yearOfDemolition, measuredHeight, storeysAboveGround etc. Values of certain schema attributes for example building class, function, usage, roof types must be defined as a code of a valid XML code list. A sample code list of all the schema attributes which must be defined as a code is available [here](https://www.sig3d.org/codelists/citygml/2.0/building/2.0/). Custom or external code list based on individual study areas can also be developed and used. Generic attributes are defined by the user to store additional information in a city object. There is no restriction in the number or the names of the generic attributes, as long as they conform to the XML syntactic rules.
@@ -46,6 +46,9 @@ Example CityGML 2.0 building model of HFT Stuttgart modeled in LOD 1,2 and 3 can
 
 # **New in CityGML 3.0 Building Data Model**
 
+CityGML 3.0 revises the LOD concept, which now allows representing the interior of a building and other CityObjects at any level of detail. LOD4, which is used for representing the interior of objects in CityGML 2.0 is removed and only the LODs 0/1/2/3 remains. The interior of objects can now be integrated with the LODs 0/1/2/3. It is also possible even to model the outside shell of a building in LOD1, while the interiors in LOD2 or 3. 
+
+**Representation of CityGML 3.0 Building in LOD 0 (Left) and LOD2 (Right) with interiors**
 
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