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Content for LOD3 |
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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
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analyzes or in visualizations for urban planning, for example in the context of citizen participation.
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Publicly available 3D models in LOD3 are therefore also rare.
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**LOD3 daata model**
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Similar to LOD2 building geometry, the CityGML 2.0 standard allows the use of MultiSurface elements to model the boundary surfaces and openings while Solid elements to model a building as a water tight geometry in LOD3.
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A XML document of CityGML 2.0 LOD3 building object with building solid geometry will look like this:
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**snippet xml lod3**
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Below figure shows a graphical representation of CityGML 2.0 LOD3 building object:
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**lod3 model sketchup with semantic label**
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To demonstrate the process of creating CityGML 2.0 LOD3 building model use of SketchUp with FME is described below:
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## **Using SketchUp with Feature Manipulation Engine (FME)**
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In order to make a conversion from Sketchup to CityGML 2.0 LOD3 using FME, the modeling process in Sketchup must meet some layering requirements:
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- All the edges must be kept in Layer0.
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- New layers must be defined using the following abbreviation name for CityGML semantic elements:
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1. ws → WallSurface
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2. gs → GroundSurface
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3. rs → RoofSurface
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4. w → Window
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5. d → Door
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6. bp → BuildingPart (optional)
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7. cls → ClosureSurface (optional)
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8. bi → BuildingInstallation (optional)
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- All polygons must be classified to its respective SketchUp layers based on above classification.
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- Parent-child elements are separated with underscore ( _ ) and elements from their ids with dash ( – ). For example, a layer "ws-1_d-1" interprets to “doors belonging to wall surface 1". In case of doors or windows, the parent boundary surface should hold all the individual elements. For example, if a wall surface (ws-1) has 2 doors and 3 windows, then the 2 doors should be put in a layer named ws-1_d-1 and the 3 windows in a layer named ws-1_w-1.
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**lod 3 model sketchup**
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A complete FME workbench along with sample input and output dataset modeled as LOD3 MultiSurface can be downloaded from **here**. The available FME workbench contains annotations for easy step by step understanding of the conversion process.
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**lod 3 FME workflow**
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>The SketchUp model is created using a local (cartesian)coordiante system. No coordiante trasnformation is done during its translation to CityGML as the purpose of this exercise is to demonstrate the conversion process. For 3D data reprojection, transformer 3D affiner can be used to define a coordinate transformation matrix. For defining a CRS, transformer coordinatesystemsetter or reprojector can be used. More info on working with coordinate systems in FME can be found from [here](https://community.safe.com/s/article/using-coordinate-systems-within-fme).
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A CityGML 3.0 LOD1 building model of the above used example building can be downloaded from **here**. An automated CityGML2-to-CityGML3 convertor is used to convert the LOD1 building model from CityGML 2.0 to CityGML 3.0.
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To correctly insert building solid either using [FME](https://gitlab.com/volkercoors/CiD4Sim/-/wikis/usefulTools/FME-Workbenches-(EN)) or a free [SolidInjector](https://github.com/tomeof/citygml-injector) please follow the [previous tutorial](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/wikis/EN/CityGML-Tutorial/chapter-2:-Building/LOD2).
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**Next Chapter** [chapter 2.4: Appearance](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/wikis/EN/CityGML-Tutorial/chapter%202:%20Building/Appearance)
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</div>
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<div>
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**Previous Chapter** [chapter 2.2: Building LOD2](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/wikis/EN/CityGML-Tutorial/chapter%202:%20Building/LOD2)
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</div> |
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\ No newline at end of file |
