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I'm looking for a way to do something very similar to the technique using the skin modifier, but with NURBS. In other words, I'm looking for a way to do something similar to a convex hull, but not necessarily convex. I want a tree-like meshing with custom branch morphing.


Example with skin modifier:
Skin modifier example

With surfaces, the make segment command f doesn't allow to do branching.

Extruding a nurbs curve only works with uniform extrusion (unless I'm mistaken), meaning you cannot morph from, say, a circle to an oval. You can only uniformely reduce the size of the extrusion shape.

Python code is welcome as an answer.

Initial curves describing the volume:
Set of circles describing a branch

Desired meshing from NURBS:
Desired nurbs meshing

Make segment unwanted result:
Unwanted result

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Blender is not known or marketed for its NURBS support, it is primarily a polygon modelling tool. While we have great modifiers like the Skin Modifier you mentioned, we don't have anything out of the box that would produce comparable NURBS surfaces.

A scripted solution also seems a bit beyond what is convenient to do in Blender, the API has limited support for generating arbitrary patch shapes that would be needed to do your Question justice.

I'd like to be proven wrong someday, or today, but for now I'd like to offer this as an interim answer and not just a cheeky comment. There are better tools for generating NURBS, consider freeCAD or any of the other free CAD/NURBS alternatives.

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  • $\begingroup$ I know that Blender isn't geared towards NURBS but it has made a lot of progress. I don't think we're so far from a solution that would satisfy this use-case. There are a lot of addons for Blender so it is possible this will emerge from the community at some point. There was a better implementation of NURBS done at the GSOC 2014, I don't know if this was integrated to the current Blender. $\endgroup$ – nantille Jun 3 '15 at 8:19
  • $\begingroup$ No the GSOC code did not make it into Blender. Previous attempts have also not made significant improvements over the past 5 years. $\endgroup$ – zeffii Jun 3 '15 at 9:35
  • $\begingroup$ I had a look at it and it seems interesting but as the name implies, it is made for CAD. My context is related to biology and visualising simulations. Then there's the communication part between FreeCAD and Blender... I'll give it a try though. Thank you. $\endgroup$ – nantille Jun 4 '15 at 15:43
  • $\begingroup$ @nantille, if there existed good solutions I would share them instantly. $\endgroup$ – zeffii Jun 4 '15 at 16:30
  • $\begingroup$ Haha no worry zeffii, your answer is appreciated. I feel like I hit the limit a bit too soon but that's just how Blender is at the moment. $\endgroup$ – nantille Jun 5 '15 at 8:46
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You can have a curve which the bevel is not uniform. In the curve panel, you have two search property (Taper object and Bevel object)

The Bevel object controls the shape of the bevel. The Taper object controls the width (radius) of the curve.

Taper object and bevel object

You can stil using a mesh (with only edges and branches) to map all your tree and then convert it to a curve (space, convert to). But there are small hickups at the joins... no miracle solution...

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You may want to employ some of the open source tools in the medical field that build branching bronchial or artery mesh or nurb surface geometries from patient scan datasets to build your geometries, then import them as mesh into blender.

Consider this 3Dslicer topic https://discourse.slicer.org/t/old-iges-segmentation/200.

Also this paper https://www.andrew.cmu.edu/user/jessicaz/publication/vascularmodel/cardiovascular.pdf should be a good jumping off point for understanding bifurcating tube structures and nurbs surfaces and the jargon that is used for better google searches, check the reference section that mentions software options.

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