Smooth calculation mystery.

Urkie

Hi,

I'm currently working on a car(ish) project where I have to make certain parts excactly how they are in the TurboCAD drawings. I stumbled on a annoying issue I really can't find a solution for.

For example; I'm making a part where I have to cut a hole with a radius of 2.5cm. The circle etc is all fine and all'. Sadly the hole shrinks as soon as I apply a (turbo)(preview)smooth. At first I thought the issue was that Maya calculates from the middle of an polygon instead of the vertex. So I applied some basic math and created a hole with a radius of 2.885cm. STILL the hole became smaller then 2.5cm. Oh my days.


Smooth.

Model.

Does anyone know a solution for this, without using boolean or a 32sided cylinder? Let me know if you have any suggestions! Also I actually swapped from (beginnerlvl)3dsMAX to Maya this week due having a macbook. So take it easy with the maya-jargon .

Thanks for reading my first post here! Wicked forum.

rebb

I don't think Subdivision Surfaces are so well suited for things that need to be super-duper-exact, they are an approximation that gets closer to the described surface the higher their subdivision level is.

So your hole might even get a tiny bit smaller still, if you increase the subdivision amount.

NURBS are much more suited for technical things that require exact precision, they were even originally invented for the requirements of the Automobile and Ship Industry.

But if this model isn't really required to have 100% accuracy, you could just eyeball it by adjusting the size of the hole while smoothing is active.

Urkie

I thought NURBS we're mostly used for architectural purposes, but I guess that makes sense for the Automobile and Ship Industry aswell. I'll give it a shot! Cheers.

Tho I still hope to find out how exactly smooth gets calculated within Maya. There should be some kind of Math behind it. I have a feeling it might come in handy in later projects eventually.

AnimeAngel

Ya NURBS is the way to go, especially in maya, for vehicles that need to be super exact.

couette

Urkie wrote: »

Tho I still hope to find out how exactly smooth gets calculated within Maya. There should be some kind of Math behind it. I have a feeling it might come in handy in later projects eventually.

The algorithm:

http://en.wikipedia.org/wiki/Catmull%E2%80%93Clark_subdivision_surface
&
http://rosettacode.org/wiki/Catmull%E2%80%93Clark_subdivision_surface

I have not tried it myself.



As others have mentioned, NURBS are the way to go if you need to model to certain dimensions or tolerances. Pure NURBS modeling may be a bit cumbersome in Maya, though. One thing you can do is use NURBS curves while you're subd modeling. The CVs of a closed NURBS curve and a CC subd surface tend to converge. For example, create a NURBS circle with an arbitrary radius, and then snap the vertices of a polygon cylinder or hole to the CVs of the circle. The cylinder or hole should subd very close to the radius of the curve. The more you divide, the closer it'll be.





For open curves, the convergence tends to fall apart at the ends or wherever you have multiple knots, but it may be useful is some instances.

EarthQuake

The more geometry your circle shape has, the less it will shrink. Something to keep in mind, 4 or 6 sides is generally lower than you want to be.

Urkie

Thanks for the reply's.

@EarthQuake: Yes I've tried that, tho its quite the hassle to model a hole that has more then six sides for me. I've just started out in Maya and my Polymodeling isnt quite 'efficient' lets say. But that's not something I'm not going to bother people with. Time will get my workflow right.

I'll get deeper in NURBS.