Choose the export by what it must preserve.
GLB is the recommended first handoff for Unreal Engine, but compatibility, editability, material needs and city structure may justify another output. This guide states what the current exporter carries and where the destination pipeline still owns the work.
Last updated: 26 July 2026
Format capabilities
| Format | Geometry & UVs | Materials & textures | Recommended use |
|---|---|---|---|
GLB.glb | Scene hierarchy, meshes, normals and UV coordinates in a binary container. | Named materials and supported image textures embedded in the file. | First choice for Unreal Engine and compact modern 3D handoff. |
glTF.gltf | Human-readable scene JSON with geometry data embedded by the current export. | Named materials and image textures embedded as data URIs. | Inspection, automation and tools that prefer open JSON-based exchange. |
OBJ + MTL.zip | Mesh positions, normals and UVs; optional merge of eligible coplanar triangle pairs into quads. | MTL plus PNG files under textures/; PBR semantics are simplified. | Broad DCC compatibility or an intermediate manual cleanup pass. |
STL.stl | Binary triangle geometry only. | No UVs, material slots or textures. | Geometry proxies, collision experiments or rapid prototyping. |
City package.zip | Separate GLB buildings and an optional GLB road network. | Each GLB carries its available materials and embedded image textures. | Organised transfer of a complete layout with independent assets. |
Compact, self-contained handoff
GLB is the binary container form of glTF. Metropolygonia exports one -ue.glb file containing the generated scene, geometry, material descriptions and supported image data. The exporter waits for pending texture images before serialising the model and verifies that referenced textures are embedded.
Choose GLB when files will move between people, folders or upload systems and a single object is easier to keep intact. It is the recommended starting format for an Unreal Engine import through Interchange. After import, verify scale, normals, material slots and UVs before duplicating the asset.
GLB does not make a final Unreal material graph. It transports a useful representation; project-specific shader authoring, collision and runtime optimisation remain downstream tasks.
Open, inspectable scene data
The current .gltf output is formatted JSON with embedded binary and image data. That keeps the browser download to one file while making the scene description readable by scripts and inspection tools.
Choose glTF when a pipeline benefits from JSON-level automation, diffable structure or a tool that specifically requests the textual form. Do not assume it is more editable than source parameters: changing generated architecture remains safer in the Metropolygonia preset, while glTF edits operate on an exported snapshot.
Compatibility with explicit sidecars
OBJ export downloads as a ZIP because a usable package requires several related files: the named .obj mesh, model.mtl, a textures/ directory of PNG images and a README. Keep them together when moving or extracting the model.
The optional quad conversion merges eligible coplanar triangle pairs. It is a limited geometric convenience, not a general retopology operation and not a guarantee that every surface becomes a clean quad grid.
- MTL records base colour, opacity, emissive, roughness and metalness values where possible.
- Supported maps use MTL directives and include texture scale and offset options.
- MTL cannot reproduce every modern PBR shader relationship.
- Texture rotation and centre transforms, and some multi-material mesh cases, may be simplified.
Choose OBJ because a destination needs it, not because it is older or appears universally safe. Run a round-trip test through the actual DCC application.
Geometry without a visual surface model
STL export contains binary triangle geometry. It intentionally omits material names, textures and UV coordinates. This makes it useful for geometry-only tasks but unsuitable for the 2 × 2 m UV or texture workflow.
Use STL for a proxy, a collision experiment or fabrication-oriented prototyping after checking that the mesh meets the target tool's manifold and thickness requirements. The generator does not certify printability, structural integrity or manufacturing tolerances.
Transfer a layout as manageable assets
The city package contains separate building GLBs, the road-network GLB when present, a JSON manifest and an Unreal-oriented README. Building files use local pivots; their placement coordinates and rotation are recorded in the manifest. Road geometry retains project-world positioning.
This is preferable to one monolithic mesh when buildings need independent placement, replacement, culling, LOD treatment or streaming. Validate one representative building first, then use the manifest to reconstruct or automate the layout according to the destination pipeline.
Choose in three questions
- Is this one building going to Unreal Engine or a modern DCC? Start with GLB.
- Does the downstream workflow explicitly need inspectable JSON, OBJ sidecars or geometry only? Choose glTF, OBJ or STL respectively and accept the stated boundary.
- Are you transferring a complete city with independently manageable buildings? Use the city ZIP rather than manually merging assets.
Whichever format you select, keep the preset as the editable procedural source and verify a known dimension after import. For the complete destination check, follow the Unreal Engine export guide.