Extracting NURBS surface data.

[Hugo Smart]

I am a student attempting to extract the NURBS surface data from SimVascular models, in order to conduct Isogeometric Analysis on bloodflow, eventually looking to model arterial stents.
Having found https://www.vascularmodel.com/ and the models contained within this repository, I have found them ideal for my project, however, due to my lack of technical understanding, I have so far been unable to extract the NURBS data (specifically, knot vectors, control points and weights).

I have tried:
- Converting the models to STEP/IGES formats directly
- Importing the models into CAD software
- Reading data directly from .vtk files
- Using the SV python installation
- Going through the source code to try and understand in what format and which files the nurbs data is being extracted to.
- Searching through this forum

None of these approaches have yielded anything substantial for me, and I am worried that I will not be able to complete my project in time for my academic deadlines if I keep attempting a wide varity of approaches as listed above. I am incredibly grateful to anyone that has taken the time to read this and could provide some sort of guidance on what technical approach I should prioritise.

Thank you,
Hugo

[David Parker]

Hello Hugo,

The models in the repository are polygonal surfaces represented using VTK data structures.

You will need to first convert the SV VTK VTP model file into STL format; you can do this using a VTK Python script. You can then read in the STL format into a CAD program that supports tessellating polygonal surfaces into NURBS patches.

Cheers,
Dave

[Hugo Smart]

Hi David,

Thank you for replying so quickly and concisely.
I see now that I was working with the incorrect assumption that the SV models were in a NURBS format, and I needed to find a way to extract this data, as a result, I did not want to 'refit' NURBS from VTK data, 'losing' information.

Thank you once again for the clarification and guidance,
Hugo