4.3.4. Managing the spatial reference system¶
When setting up a 3DCityDB instance, you have to choose a spatial reference system (SRS) by picking a spatial reference ID (SRID) supported by the database and a corresponding SRS name identifier (gml:srsName) that is used in CityGML/CityJSON exports (see and Section 1.3). These settings can be easily changed at any later time using the reference system operation.
After connecting to a 3DCityDB, the SRID and gml:srsName input fields shown in the above dialog  are assigned the current values from the database. Simply edit the fields to pick a new SRID or SRS name identifier. Since changing the SRID potentially affects all geometries in your database and thus may take a long time to complete, the SRID field is disabled per default. Click on Edit  to enable changes to this field. Use the Check button  to make sure that your new SRID value is supported by the database. The gml:srsName field provides a drop-down list of common SRS identifier encoding schemes (such as OGC URN encoding, see Section 3.3). You may pick one of these proposals (be careful to replace the HEIGHT_SRID token with the correct value if required) or enter any other value.
When changing the SRID, you can choose whether the coordinates of geometry objects already stored in the database should be transformed to the new SRID or whether only the metadata should be updated . The latter option might be enough, for example, if you accidentally picked a wrong SRID that does not match the imported geometries when setting up the database, and you simply want to correct this mistake.
Click on Apply to update the reference system information in the database according to your settings. The Restore button lets you discard any changes made to the SRID and gml:srsName fields.
If you just want to use different gml:srsName values for different CityGML exports, then instead of changing the identifier in the database before every export it is simpler to create multiple user-defined reference systems for the same SRID (cf. Section 4.7.2) and pick one for each export (cf. Section 4.5).