Defining hard corners in an indentation on a curved object

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  10 October 2010
Defining hard corners in an indentation on a curved object

For simplicity in the example, imagine that you'd want to create a sphere where the middle part is a sharply defined square indentation (inwards extrusion) while the rest of the sphere is smooth.

First you create the sphere, lets say 20x20 segments. Then you select a few adjacent polygons in the middle of the sphere and extrude them inwards. Alternatively, you first make an extrusion along the surface first, to give you a good basis for defining the rim of the extrusion, and then extrude the middle face inwards.

So far, so good. Now, when you smooth this, you'll end up with a circular hole. But we wanted a square hole, with sharply defined corners.

The only two methods through which I've succeeded in doing this is to either smooth and object first, then add the indentation (And while this works fine in such a simple project as the example I made in this post, in more advanced and irregular hard-surface objects it would take an annoying amount of planning to make this work. The other is to smooth first and then do a boolean difference operation with a square object. It goes without saying that this can result in catastrophic results, as especially more advanced meshes will require a massive amount of cleanup, if the boolean even work (Maya's Boolean tools have a track record which is quite unimpressive, at least for me), and the same problem with having to plan ahead is present in this case.

So, how do one go about defining the corners while at the same time preserving the smoothness of the objects surface? Every method I've tried have ended me up with smoothing artifacts at the corners, like bumps or edge-pinches. If you could, please post pictures showing your topology solutions

Last edited by hellspawned : 10 October 2010 at 12:39 PM.
  10 October 2010
The answer is more geometry on your base sphere. 128 segments seems to work for me, next its just a matter of adding support edges and then sliding the outer most ones to get a nice hard crease.

I selected the area i wanted for the square, then inset to create a border edge, then extrude inwards -0,1, then extrude inwards -1,0, another -0,1 then add subd modifier.


Last edited by Psyk0 : 10 October 2010 at 03:28 PM.
  11 November 2010
After many months of asking myself this very question, i have yet to find a simple way to model without artifact or bumps

you can only minimize it by making a dense mesh

but then comes the problem of alignen everything correctly by hand.

ive tried all the methods you mentioned even patch and spline modelling.

from what i can see now the best method is the preplanning/presmooth method.

but of course, it feels rediculous for such as simple thing.

but with polygons and smoothing, i dont know if there ever is a simple way
  11 November 2010
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