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# **Level of Detail (LOD) Concept**
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In CityGML, a building object can be defined in different Level Of Details (LOD). For example, in CityGML 2.0, a building can be defined as LoD 0,1,2,3 and 4. With an increasing level of detail, optional components such as geometric details, interior or exterior fittings, door and window openings, and interior spaces and their fittings are added. The same concept also applies to the other modules (CityObjects) of CityGML.
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<div align = center>
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<div>
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**A simple building represented in LOD0 (Left) to LOD4 (Right)**
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</div>
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LOD0 maps the extent of the objects on the terrain surface. In the case of buildings,
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a distinction is made between the floor plan or "footprint" of the building on the
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ground surface and the extent from a bird's eye view, which also includes the roof
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overhangs (RoofEdge). With the LOD0, the position of objects can be analyzed and
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visualized without the computational effort required for rendering three-dimensional
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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
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geometries without details of shape or equipment. For buildings, this is a flat roof
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block. LOD1 objects can be generated from their floorplans or positions by simple
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extrusion. If an aerial photo is spread over it, a realistic impression is often created.
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The LOD1 model is already suitable for propagation analyzes or planning scenarios,
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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
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given roofs, mostly using standardized roof shapes. Projections, bay windows and
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outbuildings are taken into account in this stage and modeled geometrically. An
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object in LOD2 is usually made up of a lot more individual interface elements. This
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costs additional computing time for the visualization, which can become an obstacle
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for large LOD2 models. In addition to the details of the form, the furnishing of the
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objects with individual wall coverings (textures) or the assignment of material
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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
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additional equipment elements such as chimneys and antennas, balconies, external
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stairs, pipes, lamps, etc. can be fitted. LOD3 models are therefore already very
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realistic and well suited for the visualization of object planning in manageable
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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
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detail, rooms are embedded in the building and potentially furnished with equipment
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elements and furniture. The LOD4 model is definitely suitable, for example, for simulating
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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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</div>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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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 modelling 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 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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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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example: HFT (one building) (figure from Athanasios)
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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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link to open access data set of HFT campus
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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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UML diagramm of Building Module
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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 modelling 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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one small citygml model (1 building) -> Model shall be stored in the Repository.
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example: HFT (one building) (figure from Athanasios) 
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link to open access data set of HFT campus
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UML diagramm of Building Module
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one small citygml model (1 building) -> Model shall be stored in the Repository.
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The building model defines the geometric and semantic properties of a building in CityGML. A building or a building part can be modeled as Solid (B-rep) or MultiSurface. The semantic objects for a BoundarySurface geometry in LOD2 are: RoofSurface, WallSurface, GroundSurface, and ClosureSurface.
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CityGML also defines attributes for every city object. The standard defines two types of attributes: Schema attributes and generic attributes. Schema attributes are part of the schema definition of each thematic module.
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CityGML also defines attributes for every city object. The standard defines two types of attributes: Schema attributes and generic attributes. Schema attributes are part of the schema definition of each thematic module.
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The building schema defines the attributes: function, yearOfConstruction, yearOfDemolition, measuredHeight, storeysAboveGround etc. 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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* [Chapter 1.1: CityGML Appearance Module](./chapter%201:Intro%20CityGML/Appearance)
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* [Chapter 1.1: CityGML Appearance Module](./chapter%201:Intro%20CityGML/Appearance) |
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