EN/CityGML-Tutorial/chapter-1:-Intro-CityGML.md

@@ -10,9 +10,26 @@ The following example shows a CityModel (CityGML 2.0) that makes use of several
 
 ![3D_DLM_Stoeckach](uploads/5f7b4ff3ea8229a7daa9561c753425a7/3D_DLM_Stoeckach.png)
 
-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 LGL (base DLM and LiDAR data) and the City of Stuttgart (tree cadastre and LoD2 building module). 
+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). 
+
+
+## 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)
+
+[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)
+
+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)
 
-Reference: 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)