How many sides of a polygon do you need for a perfect subd circle

pangaea

Hi Guys,

So assuming I'm modelling in modo and hit the subd button and want a perfect circle. Should I be using a 6 sided polygon or 8 sided polygon if I want a perfect circle?

Thanks

huffer

Here's a crazy idea! Make a cylinder with 6 sides and one with 8 sides, subdivide them, and compare!

pangaea

@huffer
One is mathematically the correct answer. I need to know which one is mathematically correct, your eyes can play tricks on you. 6 sided subd polygon looks a bit off to me, but 8 looks perfect. 

passerby

Define perfect. Subd is just add more geo and smoothing things. So not perfert but the more starting geo you have and the more subd iterations you have the closer to perfect it will be. But it will never be perfect.

ZacD

I believe Modo uses a flavor of Catmull–Clark subdivision, which will never give you a perfect circle, but most of the time, I feel like 32, 64, 128 is good enough, depending on the size, scale, and how close it will be to the camera. 

JedTheKrampus

8 is what I usually go for for visual correctness. If you want mathematically correct surfaces you should be using CAD or Nurbs instead of subdivision surfaces.

Vailias

Agreed with the above. Smoothing algorithms in use won't give you a mathematically perfect circle, if, for no other reason, than you'll need infinite subdivision levels to get there. 

I do find that multiples of 4 pointed shapes tend to give good results.

Bek

ZacD said:

I believe Modo uses a flavor of Catmull–Clark subdivision

  Modo has both catmull-clark (Shift+tab) or 'regular' sub-d (tab).

musashidan

Mathematics aside, 8 is traditionally used in sub-d modeling as it's very easy to cut into existing topology and gives perfectly fine results with 2 levels of smoothing.

LaurentiuN

passerby said:

Define perfect. Subd is just add more geo and smoothing things. So not perfert but the more starting geo you have and the more subd iterations you have the closer to perfect it will be. But it will never be perfect.

This is perfect to me Sorry for deviating!! https://www.youtube.com/watch?v=ZMByI4s-D-Y

peanut™

Bek said:

ZacD said:

I believe Modo uses a flavor of Catmull–Clark subdivision

  Modo has both catmull-clark (Shift+tab) or 'regular' sub-d (tab).

Thanks i always confuse them ... the who's who