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> CityGML is an open conceptual data model for the storage and exchange of virtual 3D city models. It is defined through a Unified Modeling Language (UML) object model. This UML model extends the ISO Technical Committee 211 (TC211) conceptual model standards for spatial and temporal data. Building on the ISO foundation assures that the man-made features described in the City Models share the same spatial-temporal universe as the surrounding countryside within which they reside. The aim of the development of CityGML is to reach a common definition of the basic entities, attributes, and relations of a 3D city model. This is especially important with respect to the cost-effective sustainable maintenance of 3D city models, allowing the reuse of the same data in different application fields. [^1]
> CityGML is an open conceptual data model for the storage and exchange of virtual 3D city models. It is defined through a Unified Modeling Language (UML) object model. This UML model extends the ISO Technical Committee 211 (TC211) conceptual model standards for spatial and temporal data. Building on the ISO foundation assures that the man-made features described in the City Models share the same spatial-temporal universe as the surrounding countryside within which they reside. The aim of the development of CityGML is to reach a common definition of the basic entities, attributes, and relations of a 3D city model. This is especially important with respect to the cost-effective sustainable maintenance of 3D city models, allowing the reuse of the same data in different application fields.<sup>1</sup>
In order to describe a city model, CityGML utilizes thematic modules. The base module is the CityGML Core which gets extended by defined thematic modules such as Building, Bridge, Vegetation, Transportation, WaterBody, Relief, LandUse, Appearance etc. In this tutorial, the building module will be used to explain the CityGML concepts. Examples will be given in CityGML 2.0 as most existing models are using this Version. However, the examples will be given in CityGML 3.0 XML encoding as well to see the differences of CityGML 2.0 and CityGML 3.0.
In order to describe a city model, CityGML utilizes thematic modules. The base module is the CityGML Core which gets extended by defined thematic modules such as Building, Bridge, Vegetation, Transportation, WaterBody, Relief, LandUse, Appearance etc. In this tutorial, the building module will be used to explain the CityGML concepts. Examples will be given in CityGML 2.0 as most existing tools are using this version. However, the examples will be given in CityGML 3.0 XML encoding as well to see the differences of CityGML 2.0 and CityGML 3.0.
![CityGML 3.0 Module Overview](uploads/db6d3196812b0a7306be4ac5565e13f1/fig_3.png)
......@@ -11,62 +8,59 @@ CityGML 3.0 Module Overview ([OGC document 20-066](https://docs.opengeospatial.o
The following example shows a CityModel (CityGML 2.0) that makes use of several modules including Building, Bridge, WaterBody, Vegetation, Relief, and Transportation.
<dl class="bildunterschrift">
<dt><img src="uploads/5f7b4ff3ea8229a7daa9561c753425a7/3D_DLM_Stoeckach.png" alt="Bildbeschreibung" title="Kap-LoD-1-Gebäudehöhen-ALKIS3D"></dt>
<dd> City Model Stuttgart Stöckach </dd>
</dl>
<dl>
<dt>
CityGML Model Stuttgart-Stöckach, the model itself was created by L. Rothengass as prt of his Master Thesis at HFT Stuttgart using the software [3dfier](https://github.com/tudelft3d/3dfier) and data provided by the State Office for Spatial Information and Land Development (LGL BW) (base DLM and LiDAR data) and the City of Stuttgart (tree cadastre and LoD2 building module).
![Bildbeschreibung](uploads/5f7b4ff3ea8229a7daa9561c753425a7/3D_DLM_Stoeckach.png "Kap-LoD-1-Gebäudehöhen-ALKIS3D")
</dt>
<dd>City Model Stuttgart Stöckach</dd>
</dl>CityGML Model Stuttgart-Stöckach, the model itself was created by L. Rothengass as prt of his Master Thesis at HFT Stuttgart using the software [3dfier](https://github.com/tudelft3d/3dfier) and data provided by the State Office for Spatial Information and Land Development (LGL BW) (base DLM and LiDAR data) and the City of Stuttgart (tree cadastre and LoD2 building module).
## CityGML Core
The following UML diagram defines the CityGML top level class hierarchy (CityGML 2.0 standard document, fig. 23, p51).
The following UML diagram defines the CityGML top level class hierarchy (CityGML 2.0 standard document, fig. 23, p51).
![image](uploads/c0637b17c8b839570b05ca5f4f235a1c/image.png)
A _City Model_ is a collection of _cityObjectMembers_. Each CityGML Module defines specific _CityObjects_ such as _Building_ objects, _Vegetation_ objects etc. Every _CityObject_ has a fixed set of specific attributes as specified in the UML model, and an _Appearance_ do define its visual properties. _GenericAttributes_ can be used to define additional attributes that are not explicitly specified in the UML model itself.
The XML encoding of the UML diagram is defined in an XML schema. In CityGML version 2.0, the XML schema part of the CityGML standard document. An example of a typical XML document - the CityModel - is sketched here:
<?xml version="1.0" encoding="UTF-8"?>
<core:CityModel xmlns = … >
<core:cityObjectMember>
<bldg:Building> … </bldg:Building>
<bldg:Building> … </bldg:Building>
<bldg:Building> … </bldg:Building>
<!-- Terrain -->
<dem:ReliefFeature> … </dem:ReliefFeature>
<!– Lake -->
<wtr:WaterBody> … </wtr:WaterBody>
…
</core:cityObjectMember>
</core:CityModel>
In CityGML 3.0, the UML model is defined in the conceptual model standard. Multiple encodings can exist to encode the conceptual model. One encoding is the XML encoding. With CityJSON, another encoding of the conceptual model is available.
## References:
The XML encoding of the UML diagram is defined in an XML schema. In CityGML version 2.0, the XML schema part of the CityGML standard document. An example of a typical XML document - the CityModel - is sketched here:
```plaintext
<?xml version="1.0" encoding="UTF-8"?>
<core:CityModel xmlns = … >
<core:cityObjectMember>
<bldg:Building> … </bldg:Building>
<bldg:Building> … </bldg:Building>
<bldg:Building> … </bldg:Building>
<!-- Terrain -->
<dem:ReliefFeature> … </dem:ReliefFeature>
<!– Lake -->
<wtr:WaterBody> … </wtr:WaterBody>
…
</core:cityObjectMember>
</core:CityModel>
```
In CityGML 3.0, the UML model is defined in the conceptual model standard. Multiple encodings can exist to encode the conceptual model. One encoding is the XML encoding. With CityJSON, another encoding of the conceptual model is available.
## References:
[OGC CityGML standards](https://www.ogc.org/standards/citygml)
### CityGML Version 3.0
[OGC City Geography Markup Language (CityGML) Part 1: Conceptual Model Standard, OGC document 20-010](https://docs.ogc.org/is/20-010/20-010.html)
1. [OGC City Geography Markup Language (CityGML) 3.0 Conceptual Model Users Guide, OGC document 20-066](http://www.opengis.net/doc/UG/CityGML-user-guide/3.0)
[^1] [OGC City Geography Markup Language (CityGML) 3.0 Conceptual Model Users Guide, OGC document 20-066](http://www.opengis.net/doc/UG/CityGML-user-guide/3.0)
[OGC City Geography Markup Language (CityGML) Part 1: Conceptual Model Standard, OGC document 20-010](https://docs.ogc.org/is/20-010/20-010.html)
[Kutzner, T., Chaturvedi, K. & Kolbe, T.H. CityGML 3.0: New Functions Open Up New Applications. PFG 88, 43–61 (2020). https://doi.org/10.1007/s41064-020-00095-z](https://doi.org/10.1007/s41064-020-00095-z)
### CityGML Version 2.0
[OGC City Geography Markup Language (CityGML) Encoding Standard, OGC document 12-019](https://portal.ogc.org/files/?artifact_id=47842)
L. Rothengass: Generierung und Evaluierung dreidimensionaler Landschaftsmodelle für eine CFD-Windsimulation, Master-Thesis, Vermessung, HFT Stuttgart, SS 2018, Gutachter: Herr Prof. Coors, HFT Stuttgart und Frau Dr. Wild-Pfeiffer, Landesamt für Geoinformation und Landentwicklung Baden-Württemberg (LGL BW) (in german)
L. Rothengass: Generierung und Evaluierung dreidimensionaler Landschaftsmodelle für eine CFD-Windsimulation, Master-Thesis, Vermessung, HFT Stuttgart, SS 2018, Gutachter: Herr Prof. Coors, HFT Stuttgart und Frau Dr. Wild-Pfeiffer, Landesamt für Geoinformation und Landentwicklung Baden-Württemberg (LGL BW) (in german)
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