What's the meaning of preRotation , postRotation , rotation in FBX?

[CaichaoGitHub]

Hi guys
i'm loading a fbx model using Assimp , but i found some extension in Node Tree
in FBX converter:

in Processed Model:

Would anyone explain how to handle the extension info please?

[RichardTea]

The FBX format stores node transforms using an expanded sequence of transforms. These aiNodes represent that sequence.
They are simply aiNode that have no mesh and a single child for the next stage of the FBX transform.

Either treat them the same as any other aiNode that has no mesh, or multiply the transforms together to collapse them into a single aiNode.
I believe there's an FBX importer property to get assimp to do the latter.

As I understand it, FBX does this because it was originally created for motion capture, and it's useful to have the decomposed transform when working with motion capture data because it's not possible to decompose a transform matrix back into the original set of rotation etc, only an equivalent.

[AndrewChan2022]

The FBX format stores node transforms using an expanded sequence of transforms. These aiNodes represent that sequence. They are simply aiNode that have no mesh and a single child for the next stage of the FBX transform.

Either treat them the same as any other aiNode that has no mesh, or multiply the transforms together to collapse them into a single aiNode. I believe there's an FBX importer property to get assimp to do the latter.

As I understand it, FBX does this because it was originally created for motion capture, and it's useful to have the decomposed transform when working with motion capture data because it's not possible to decompose a transform matrix back into the original set of rotation etc, only an equivalent.

I use this to collapse the node:
importer.SetPropertyBool(AI_CONFIG_IMPORT_FBX_PRESERVE_PIVOTS, false);