USD and Alembic Files
Vertexix opens USD files (.usd, .usda, .usdc, .usdz) and Alembic files (.abc) in every edition, the same way as any other model: Load Mesh, the File menu, or a drop onto the window. Regular and Ultra also write USD.
Opening a USD file
Everything below comes in from a USD file:
- Every mesh in the file, at the position, turn and scale it has in the scene. Quads and larger polygons stay as they were authored; nothing is split into triangles.
- Normals, every UV set (under its own name, such as st) and vertex colours.
- Materials, face by face. A mesh whose faces use different materials (USD's GeomSubsets) arrives with each face on its own material.
- UsdPreviewSurface material values and textures: base colour, metallic, roughness, normal, emissive, occlusion and opacity.
- The textures inside a .usdz. A .usdz packs its textures into the one file; they are read from there, so nothing needs to sit beside it. A .usd, .usda or .usdc looks for its textures where the file says, relative to the file.
The model always arrives upright and in metres: a file written Z-up (Blender's way) is turned so its up is Vertexix's up, and a file written in centimetres (USD's own default) is scaled to metres.
Not read from USD:
- animation, skeletons and blend shapes — the model comes in as it stands;
- texture placement inside a material (a texture moved, turned or tiled by the material itself);
- MaterialX and OpenPBR materials — their meshes arrive with a plain grey material, ready to paint or bake onto.
Opening an Alembic file
Alembic is a format for geometry. It is common for files from Maya, Houdini and Blender. Vertexix reads:
- The first frame of every polygon mesh in the file, and of every subdivision surface (its cage — the polygons you would edit, not the smoothed result).
- The position, turn and scale each mesh has in the scene; quads and larger polygons as authored.
- Normals and the first UV set.
- Face sets as materials. Alembic has no material settings, only named groups of faces; each name becomes a material of that name (grey, ready to paint or bake onto), and faces in no group go on DefaultMaterial.
Alembic files carry no unit, so the numbers come in exactly as written. A file from a program that works in centimetres arrives a hundred times bigger than the same model in metres.
Not read from Alembic:
- animation beyond the first frame;
- curves and points (hair, particles);
- UV sets after the first;
- the old HDF5 kind of Alembic file. Most programs have written the newer kind, Ogawa, for years. If an older .abc will not open, export it again from the program that made it.
Writing USD (Regular and Ultra)
Export Mesh offers USD in three forms. They share one row in Settings > Export, USD (usdz, usdc, usda).
| Form | What it is | Textures |
|---|---|---|
| .usdz | One file, ready to send or open on a phone or in a viewer | Packed inside the file |
| .usdc | Binary USD | PNG files beside the model |
| .usda | Text USD, readable in any text editor | PNG files beside the model |
A USD export carries:
- the mesh with its polygons as they are (USD keeps quads);
- its normals, its first UV set, and its vertex colours;
- each material as a UsdPreviewSurface, with its values and textures: base colour, metallic, roughness, normal, emissive, occlusion and opacity.
The file says it is in metres and Y up, so other programs show it at the size and the way up you see it in Vertexix. A USD file that leaves the unit out is read as centimetres, which would shrink the model a hundred times anywhere else.
Only the first UV set is written, and nothing of a rig. For a rigged model, use Exporting Rigged glTF.