You can export Unreal Engine and Twinmotion (DATASMITH) data from CityEngine to the Unreal Engine Editor and Twinmotion. This is typically used for architectural and design visualization workflows, but you can also use it for games and other tasks.
- Exporting Unreal data is only available on Windows.
- To export Unreal data in CityEngine, the Unreal Engine Launcher must be installed first.
- The CityEngine Model Loader Project is no longer needed and will be removed from the Unreal Engine Launcher.
In addition to the general export options, the following options are available for DATASMITH export:
Export Twinmotion Compatible
Makes the DATASMITH export compatible with Twinmotion. The export uses Unreal Base Materials, which are compatible with both Twinmotion and Unreal (the Use Unreal Base Materials export option must be set to true). It also disables features that are not compatible with Twinmotion:
Applies global offset for generated geometry for x, y, and z axes (Cartesian coordinate values).
Sets how the resulting meshes are merged:
Sets how instancing is handled:
Exports metadata when Mesh Merging is set to either Per Initial Shape or Per Initial Shape by Material. The following are the metadata export options:
The exported metadata is attached to the root object of each initial shape in Unreal.
Exports terrain layers to Unreal Engine Landscapes. The following options are supported:
Use Unreal Base Materials
Uses Unreal Base Materials as the primary material for all exported materials. These predefined materials are compatible with both Twinmotion and Unreal. They support the following CityEngine material attributes:
Use Texture Atlases
Enables texture atlases that combine exported textures and reduce the number of materials. Texture atlases typically have the greatest impact when used on slower hardware, for example, on mobile VR devices such as the Oculus Quest.
Enables export of level of detail (LOD). Exporting LOD is only enabled when exporting per initial shape.
The name of the CGA attribute that specifies the LOD. The attribute must have an Enum annotation. For each element of the Enum annotation, a derivation is triggered when the LOD attribute is set to this element value.
The following example generates three LODs per initial shape:
Note:If the attribute is defined in multiple CGA files, it must have the same elements (LODs).
The semantic order of the LOD Attribute values.
For example, if the LOD Attribute option is defined as follows, the order is ascending, as the lowest level of detail is defined first.
Defines how default objects are exported.
Mapping between CityEngine and Unreal entities
Materials are mapped to Unreal by passing CGA material attributes to an Unreal material instance, which is based on a certain primary (or parent) material.
By default, appropriate primary materials are generated that handle the mapping from CGA material attributes to Unreal material attributes (see also Default primary materials).
Custom primary materials
A custom primary material can be assigned by setting the material.shader CGA attribute to the corresponding Unreal material path, for example, /Game/Materials/CityEngineMaterials/M_CE_MyMaterial.
Each CGA material attribute is exported and can be accessed in Unreal using a material parameter with a specific name and data type. The following table lists the CGA material attributes and their respective Unreal parameter name and type:
|CGA attribute||Unreal parameter name||Unreal type||Notes|
For the OpacitySource value, select from the following:
Default primary materials
By default, an appropriate primary material (opaque, transparent, or masked) is generated during export, based on the following rules:
- If material.opacity is smaller than 1 or material.opacitymap is set
- and the opacitymap.mode is blend, a Transparent primary material is used.
- and the opacitymap.mode is masked, a Masked primary material is used.
- Otherwise the Opaque primary material is used.
Unreal Engine sorts transparency per actor. Exporting overlapping transparent actors leads to rendering artifacts. Masked binary opacity is not affected by this limitation.
Default material attribute mapping
The default primary materials map the CGA material attributes roughly to a physically based Unreal Material. If material.shader is set to CityEnginePBRShader (this happens automatically if, for example, an inserted glTF model is exported), the default primary materials in Unreal use the PBR material attributes (roughness, metallic, and emissive).
The specular color is not used in Unreal. The specular color in Unreal depends on the base color and how metallic the material is.