NURBS import/export

Before I go trying to build out support for NURBS in the FBX importer/exporter, is anyone aware of an existing functional workflow for the import/export of NURBS curves? FBX supports this, but it’s been left out of the plugin for some reason. OBJ also supports it, but it’s not functioning properly at the moment. IGS support seems to be missing, and USD scenes can’t be imported. Perhaps there’s a format/configuration I am overlooking.


I work with curves a lot going back and forth between Rhino and Blender. I tend to use OBJ, but it’s hacky. On importing, the scene has to have a mesh object in order for the curves to import. They do match the Rhino output. When exporting objs, i export polylines and need to rebuild nurbs curves based on the vertices. The workflow is not completely accurate though.

When i did need completely accurate result, I had to write a small script because the weight wasn’t getting picked up properly by the OBJ importer. This was a few years back at v 2.78, so not sure if there’s been any change with the current OBJ importer.

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I am able to re-import objs (exported from blender) containing nurbs without any extant mesh object, but the paramaterisation is destroyed; the curve is approximated by a dense degree 1 curve. This is 2.83.

This is unrelated to NURBS but just a heads up for FBX in general.
I saw a Developer Update for Godot where Gordon McPherson said he did a lot of work on the FBX import and export compatibilities in Godot which indirectly Blender’s exporter was also going to benefit a lot from (he mentioned that it could eliminate problems with Maya exchanges).

Don’t know how much of this is already done or went into Blender already but he mentioned that he is glad for anyone helping or asking him about this because it was just so much work and he wants anyone to benefit from it. :slight_smile:

Just posting this here, for the chance that it maybe is something that could impact your work.
If not - just ignore this post. :smiley:

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Very interesting. I might ping him, thank you.

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As far as I knew this was working, could you report a bug?

sure, it’s trivial to reproduce

Any updates on the subject? I am looking for the best method to export (nurbs) curves to Rhino. Is OBJ still the best practice?

I’m a +1 on that.

I’mma start looking on my side,

So it would be about expanding on rB31d480174a8c

I use both obj and dxf to import curves from Rhino.
It depends how the curves are build in cad, but often the curves have missing parts (i guess higher degree which is not supported)?

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