7.4 File format

ASAM OpenMATERIAL 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 supports the 3D model file formats glTF, FBX, and USD with the following considerations:

glTF

ASAM OpenMATERIAL 3D models 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.

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, see Coordinate systems. While modeling, the ASAM OpenMATERIAL 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

Although FBX lacks a formal specification, ASAM OpenMATERIAL 3D models in FBX format SHALL be compatible with the official AUTODESK FBX SDK.

USD

ASAM OpenMATERIAL 3D models 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 geometry specification, +Z SHALL be used as the up axis.