| ... | ... | @@ -14,19 +14,19 @@ In CityGML, a building object can be defined in different Level Of Details (LOD) |
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LOD0 maps the extent of the objects on the terrain surface. In the case of buildings, a distinction is made between the floor plan or "footprint" of the building on the ground surface and the extent from a bird's eye view, which also includes the roof overhangs (RoofEdge). With the LOD0, the position of objects can be analyzed and visualized without the computational effort required for rendering three-dimensional bodies. An example LOD0 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD0.gml).
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LOD0 maps the extent of the objects on the terrain surface. In the case of buildings, a distinction is made between the footprin of the building on the ground surface and the extent from a bird's eye view, which also includes the roof overhangs (RoofEdge). With the LOD0, the position of objects can be analyzed and visualized without the computational effort required for rendering three-dimensional bodies. An example LOD0 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD0.gml).
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LOD1 is the level of the so-called "block model". It maps the model objects in simple geometries without details of shape or equipment. For buildings, this is a flat roof block. LOD1 objects can be generated from their floorplans or positions by simple extrusion. If an aerial photo is spread over it, a realistic impression is often created. The LOD1 model is already suitable for propagation analyzes or planning scenarios, even if it does not yet have the accuracy and realism of a LOD2 model. An example LOD1 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD1.gml).
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LOD1 is the level of the so-called "block model". It maps the model objects in simple geometries without details of shape or equipment. For buildings, this is a flat roof block. LOD1 objects can be generated from their footprints or positions by simple extrusion. If an aerial photo is spread under it, a realistic impression is often created. The LOD1 model is already suitable for propagation analyzes or planning scenarios, even if it does not yet have the accuracy and realism of a LOD2 model. An example LOD1 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD1.gml).
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In LOD2, the objects are given a form that is closer to the real world. Buildings are given roofs, mostly using standardized roof shapes. Projections, bay windows and outbuildings are taken into account in this stage and modeled geometrically. An object in LOD2 is usually made up of a lot more individual interface elements. This costs additional computing time for the visualization, which can become an obstacle for large LOD2 models. In addition to the details of the form, the furnishing of the objects with individual wall coverings (textures) or the assignment of material properties come into play at this level of detail. An example LOD2 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD2.gml).
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In LOD2, the objects are given a form that is closer to the real world. Buildings are given roofs, mostly using standardized roof shapes. Projections, bay windows and outbuildings are taken into account in this stage and modeled geometrically. An object in LOD2 is usually made up of a lot more individual interface elements. This costs additional computing time for the visualization, which can become an obstacle for large scale LOD2 models. In addition to the details of the form, the furnishing of the objects with individual wall coverings (textures) or the assignment of material properties come into play at this level of detail. An example LOD2 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD2.gml).
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In the third level of detail, LOD3, buildings are given doors and windows and additional equipment elements such as chimneys and antennas, balconies, external stairs, pipes, lamps, etc. can be fitted. LOD3 models are therefore already very realistic and well suited for the visualization of object planning in manageable scenes. An example LOD3 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD3.gml).
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The last level of detail, LOD4, now also models the interior of the building. At this level of detail, rooms are embedded in the building and potentially furnished with equipment elements and furniture. The LOD4 model is definitely suitable, for example, for simulating the spread of pollutants within buildings or for planning and calculating escape routes. An example LOD4 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD4.gml).
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The last level of detail, LOD4, also models the interior of the building. At this level of detail, rooms are embedded in the building and potentially furnished with equipment elements and furniture. The LOD4 model is definitely suitable, for example, for simulating the spread of pollutants within buildings or for planning and calculating escape routes. An example LOD4 model of a simple building can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/blob/master/Buch-3D-Stadtmodelle/Kap-4/TWINHOUSE_LOD4.gml).
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Other [example data set](https://schemas.opengis.net/citygml/examples/2.0/building/) in CityGML 2.0 LoD0 to LoD4 is available at the OGC CityGML 2.0 standard repository.
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LOD1 and LOD2 are the most common level of details produced by users globally and used in different applications. For some applications, such as noise simulation, an abstract model or a low level of detail (LOD1) is often useful for the analysis and modeling of entire urban areas. In case of urban energy simulation in which individual buildings are simulated, LOD2 models are often used because of its geometrical detail of roof surfaces as well as the introduction of semantic properties. LOD1 and LOD2 models of various cities and districts are usually made available as [open data](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/wikis/DE/Open%20Data). In contrast, due to the high effort involved in creating LOD3 and LOD4 models are often not available for entire urban areas or at most they are available in small excerpts or individual building.
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LOD1 and LOD2 are the most common level of details produced by users globally and used in different applications. For some applications, such as noise simulation, an abstract model or a low level of detail (LOD1) is often useful for the analysis and modeling of entire urban areas. In case of urban energy simulation in which individual buildings are simulated, LOD2 models are often used because of higher geometrical detail as well as the introduction of semantic properties. LOD1 and LOD2 models of various cities and districts are usually made available as [open data](https://transfer.hft-stuttgart.de/gitlab/coors/3d-stadtmodelle/-/wikis/DE/Open%20Data). In contrast, due to the high effort involved in creating LOD3 and LOD4 models, they are often not available for entire urban areas or at most they are available in small excerpts or individual building.
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## **Coordinate Reference System (CRS)**
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| ... | ... | @@ -56,7 +56,7 @@ To integrate different spatial datasets in a single CityGML document, a correct |
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## **CityGML 2.0 Building Data Model**
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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
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(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 with a property of boundedBy. 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.
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(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 with a property of boundedBy. 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.
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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.
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| ... | ... | @@ -66,11 +66,11 @@ The CityGML standard also defines attributes for every CityObject. The standard |
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</div>
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Further info on the CityGML building data model, its XML schema definition (XSD) and conformance requirements are available in the [CityGML 2.0 standard document](https://portal.ogc.org/files/?artifact_id=47842) Ch. 10 section 10.3.
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Further info on the data model of CityGML building module, its XML schema definition (XSD) and conformance requirements are available in the [CityGML 2.0 standard document](https://portal.ogc.org/files/?artifact_id=47842) Ch. 10 section 10.3.
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XML encoding of the CityGML building data model can be found [here](https://schemas.opengis.net/citygml/building/2.0/building.xsd) as a XSD document.
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XML encoding of the CityGML building data model can be found [here](https://schemas.opengis.net/citygml/building/2.0/building.xsd) as an XSD document.
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Example CityGML 2.0 building model of HFT Stuttgart modeled in LOD 1,2 and 3 can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/neqmodplus/neqmodplus-steinbeis/-/wikis/NeqModPlus/NeqModPlus/HfT_Campus_CityGML_2.0_Models). Due to privacy reasons, LOD4 model of HFT Stuttgart buildings are not shared publicly.
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Example CityGML 2.0 building model of HFT Stuttgart in LOD 1,2 and 3 can be downloaded from [here](https://transfer.hft-stuttgart.de/gitlab/neqmodplus/neqmodplus-steinbeis/-/wikis/NeqModPlus/NeqModPlus/HfT_Campus_CityGML_2.0_Models). Due to privacy reasons, LOD4 model of HFT Stuttgart buildings are not shared publicly.
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<div align=center>
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| ... | ... | @@ -100,7 +100,7 @@ CityGML 3.0 revises the LOD concept, which now allows representing the interior |
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</div>
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CityGML 3.0 also revising the data model of Building modules. New super(abstract) classes are introduced to inprove interoperability with other standardized data models such as IFC. First _AbstractConstruction_ class as subclass of _AbstractOccupiedSpace_ is introduced which is associated with the different thematic surfaces (previously boundary surfaces in CityGML 2.0). CityObjects such as buildings, bridges, and tunnels, are defined as subclasses of the class _AbstractConstruction_. Furthermore, a new feature type AbstractConstructiveElement is introduced and corresponding subclasses for example BuildingConstructiveElement is defined to allow easy mapping of constructive ements such as IfcWall, IfcBeam, IfcSlab etc. from BIM data sets modeled in IFC standard. Another new class _AbstractBuildingSubdivision_ which is modeled as a subclass of _AbstractLogicalSpace_ is introduced to model BuildingUnit and Storey for representing real world building units (e.g apartments) and building storeys. Class _AbstractBoundarySurface_ from CityGML 2.0 is now revised as _AbstractThematicSurface_ have two subclass of AbstractConstruction and FillingSurface with a property of boundary. Doors and Windows which were elements of AbstractOpening class in CityGML 2.0 are represented as filling elements in CityGML 3.0 in addition to the classes WindowSurface and DoorSurface introduced to represent filling surfaces. Similarly GroundSurface, RoofSurface, WallSurface, ClosureSurface etc. are modeled as ConstructionSurface in CityGML 3.0. A simplified excerpt of CityGML 3.0 building data model is shown below as a UML diagram.
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CityGML 3.0 also revising the data model of Building module. New super(abstract) classes are introduced to improve interoperability with other standardized data models such as IFC. First _AbstractConstruction_ class as subclass of _AbstractOccupiedSpace_ is introduced which is associated with different thematic surfaces (previously boundary surfaces in CityGML 2.0). CityObjects such as buildings, bridges, and tunnels, are defined as subclasses of the class _AbstractConstruction_. Furthermore, a new feature type AbstractConstructiveElement is introduced and corresponding subclasses for example BuildingConstructiveElement is defined to allow easy mapping of constructive elements such as IfcWall, IfcBeam, IfcSlab etc. from BIM datasets modeled in IFC standard. Another new class _AbstractBuildingSubdivision_ which is modeled as a subclass of _AbstractLogicalSpace_ is introduced to model BuildingUnit and Storey for representing real world building units (e.g apartments) and building storeys. Class _AbstractBoundarySurface_ from CityGML 2.0 is now revised as _AbstractThematicSurface_ have two subclass of AbstractConstruction and FillingSurface with a property of boundary. Doors and Windows which were elements of AbstractOpening class in CityGML 2.0 are represented as filling elements in CityGML 3.0 in addition to the classes WindowSurface and DoorSurface introduced to represent filling surfaces. Similarly GroundSurface, RoofSurface, WallSurface, ClosureSurface etc. are modeled as ConstructionSurface in CityGML 3.0. A simplified excerpt of CityGML 3.0 building module data model is shown below as a UML diagram.
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<div align=center>
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