A Blender add-on to import, edit and export new instances of CityJSON-encoded 3D city models. All buildings' levels of detail (LoD), attributes and semantic surfaces are stored and can be accessed via Blender's graphical interface.

This Addon is a fork of Konstantinos Mastorakis's Project UP3DATE which can be found here. It was further developed and changed to serve the special purpose we had in mind for it. This purpose is to gain a tool for editing the 3D models of individual buildings for our 3D-City-Model, to add more detail and to manually texture buildings of special importance.

Changes to the original include the addition of support for the import and export of textured models. We also added context menus in both Object-Mode and Edit-Mode to facilitate easier assignment of SurfaceTypes.

This add-on was originally developed by Konstantinos Mastorakis (konmast3r) as part of their research orientation project for the MSc Geomatics programme of TU Delft. Its functionality was further developed for the needs of their MSc thesis An integrative workflow for 3D city model versioning

The current iteration of the addon was developed using:

• Blender Version 3.5
• CityJSON v1.1.2

It has been tested to work in Blender 4.2

1. Download this repository as zip (through GitHub this can be done through the Clone or download > Download ZIP button).

2. Run Blender and go to Edit > Preferences > Add-ons and press the Install... button.

3. Select the downloaded ZIP and press Install Add-on from File....

4. Enable the add-on from the list, by ticking the empty box next to the add-on's name.
   (Optional: If you wish to update to a newer version, un-tick and tick again the add-on to reload it!)

• If you are unfamiliar with CityJSON we strongly advise you to first explore the format as you otherwise won't understand the options you will be given by this addon! You can do so on the official Website.

Go to File > Import > CityJSON (.json) and navigate to the directory where the CityJSON file is stored and open it. Make sure to check or uncheck the option for texture import in the import menu acccording to your data.

• The first imported CityJSON file will define the geographical origin of the scenes coordinate system.
• Each import after the first will be set relative to this set origin.

This addon is intended to be used in a way where you, the user, import a CityJSON geometry e.g. a ground surface of a building as a first step of any workflow. Blender is not a GIS, so we do not have proper ways of georeferencing objects that have been made in a "standard" .blend file. So please always start with some form of a referenced object or otherwise your spend time creating a detailed Object goes to waste. It is possible to create/import new objects in a scene that has been created by importing a valid CityJSON model first. Just remember to add all semantics to it before exporting or otherwise there will be errors in writing the file (as described below).

• enable Developer Extras in the blender preferences to see the custom properties you will add

In order to be able to export objects correctly the following steps need to be followed:

1. In Object Mode right-click the object and select the option set initial attributes. This initializes all the custom properties you will be able to set later. You should always start with this step, even if you import an object you have previously given these attributes. The assigned values will not be overwritten, so no worries there.

2. Now, still in Object Mode, you can assign values for the ObjectType (set Construction). Use the context menu options to do so respectively. The Metadata for LOD can be changed manually in the custom properties of the object.

3. After you have assigned the cityJSONType attribute, which declares the Object as a Bridge, Building etc., you can switch into Edit Mode to assign SurfaceTypes to your geometry. This is done by selecting a face, right-click to open the context menu and selecting the desired SurfaceType. You can also select multiple surfaces at the same time and the tool will create an individuell surface for every single one. If the polygons do not yet have a material you first need to create one yourself or by using the calculateSemantics function in Object Mode. It will calculate the most probable semantic type based on the face normals.

4. If you wish to add Textures you can do so by altering existing materials.

We strongly advise you to declare a separate material for every surface as we intended to use this addon for texturing and that capability hinges on having a material for every face.

To export your Object simply go to File > Export > CityJSON (.json). Again, make sure to check or uncheck the option for texture export in the export menu acccording to your data.

If you would like to use Point Clouds as a reference for modelling your CityJSON Objects we can recommend another Addon called Point Cloud Visualizer by Jakub Uhlík available on Blender Market (75$).

Disclaimer: We have no association with the developer, we simply regard his software as useful in our workflows.

1. You will need your structure and a pointcloud which has been clipped to the bounding box of the structure. A small buffer is recommended though. This should make sure that the center of your structure is also the center of your point cloud.
2. Import the CityJSON file and add an empty plane axis in its center in the x-y dimension. The z-axis placement should be at the height 0 which you can get by subtracting the z-parameter in the custom properties of the world properties of your project. This is nessecary because CJE places the first imported object at local height zero to facilitate easier modelling with relative measurements. I may change that in the future.
3. Now follow the instructions in the PCV Documentation
4. When you import an LAS file, for example, its geo-coordinates will be shifted to place it in a local space. The orientation will remain correct. This offsetting is a litte rough however. To align it perfectly use the option Center Origin in the edit subsection.
5. Happy modelling.