SubD advice

As I am doing a SubD boat hull modeling test, I run into a crease issue.
It happens in corners where also normal edges meet a crease.

Can you please direct me to a tutorial or advice how to handle this correctly?
The rest of the hull is already quite nice.

Thank you in advance.

Some other images of the rest of the hull:

The original boat:

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Press Tab key (or type SubDDisplayToggle) to switch SubD display from smooth mode to flat mode (a.k.a. box mode). Take good look at your model - I bet it is messed up in those spots.

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Nope, I checked that already and from that perspective it looks perfect.

It appears that behavior is inherent in SubD where three creases meet, two exterior and one interior,.or two interior and one exterior. Simple example attached: SubD Funny 1.3dm (1.9 MB)
Added: The behavior does not always occur. See the post below.

SubD appears to have some limitations for precision modeling of surfaces.

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Hi David,
Thank you for your feedback. I was already afraid for your answer.
It would be nice if a developer can reflect on this.

The problem does not always occur. A different example which behaves as expected.
SubD No Funny.3dm (1.9 MB)

I think three creases making a corner, plus one or more smooths hitting that same vertex, is the tough one.


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What do you mean by " one or more smooths hitting that same vertex"? Edges which are not creases?

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Hi David - it looks like the ugly thing happens where there are smooth and creased edges converging:


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try beveling those corners instead of creasing them.


The design intent/need is sharp edges, not rounded edges.

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Overbuild, then convert to nurbs and trim as needed.

No need to force subd in a place where nurbs works better.

Yes, that seems to be problematic; when three creases meet one or more smooth edges.

Hi Kyle,
Thank you for your input. I am testing now bevels and it is a soft crease then. The same as soft- and hard creases in good old T-Splines.
This might work and still I think that creases should also work if possible.
However, for this specific motor boat example I see that SubD is then better for the superstructure as the rough hull can perfectly be modeled with Nurbs strakes and then add the aft body propulsion details later separately.

What you’re really looking for is Edge Weighting where by selecting an edge and basically influencing how it affects the surrounding topology. Think of this as like tangency/curvature influence when modeling with NURBS.

In most other SubD/Polygonal software this is possible (Blender, Modo, Maya…etc). The Rhino team knows of this “limitation” and have said as much. If there will be the addition of this process is kind of a TBD right now. So basically it’s not a limitation of SubD modeling as much as it is just showing where things are with how it’s currently implemented in Rhino.


Thank you for your valuable reply Arthur.

Keep in mind you can crease in SubD, then convert to Nurbs and fillet or blend the resulting Nurbs surfaces to develop further.

Subd “filets” are not super precise… and in a lot of cases you are better served leaving the fiddly transition surfaces to be done in Nurbs once the main form development is done in SubD.

Remember, SubD and Nurbs play very nicely together. Make sure you are using the right (and best) tool for the intended job.