7.4 File format
ASAM OpenMATERIAL 3D does not define its own 3D model format. However, the geometry specification defines coordinate systems, units, node hierarchies, and more, which can be applied across different 3D model formats.
ASAM OpenMATERIAL 3D supports the 3D model file formats glTF, FBX, and USD with the following considerations:
- glTF
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3D models of ASAM OpenMATERIAL 3D in glTF format shall comply with the official glTF specification. The glTF specification has two delivery options: glTF + bin + textures, and the container format glb. Both delivery options are supported in ASAM OpenMATERIAL 3D.
The glTF coordinate system is right-handed, with +Y as the up axis, +Z as forward, and -X as right. The front of a glTF asset faces +Z.
This setup differs from how coordinate systems are defined in ASAM OpenMATERIAL 3D, see Coordinate systems. While modeling, the ASAM OpenMATERIAL 3D coordinate definitions shall be used. During export to and import from glTF, a coordinate transformation shall be applied to conform with the glTF specification. Common modeling tools like Blender handle this conversion automatically.
- FBX
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Although FBX lacks a formal specification, 3D models of ASAM OpenMATERIAL 3D in FBX format shall be compatible with the official AUTODESK FBX SDK.
- USD
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3D models of ASAM OpenMATERIAL 3D in USD format shall comply with the official USD specification.
The USD coordinate specification allows either +Y or +Z as the up axis, defined in the upAxis metadata. To adhere to the ASAM OpenMATERIAL 3D geometry specification, +Z shall be used as the up axis.