Sharp edges on round surfaces

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  02 February 2018
Sharp edges on round surfaces

Hello everyone!

I know this may be absolutely basic to a lot of you, but it's a problem that has been bothering me for way too long now and I'm still not able to decently fix this issue.

I've been in a lot of situations where I wanted to have a rectangular shape with sharp edges (like an extrusion or cut-out) on a smooth or round surface. I have prepared a really basic example here:

Now if I want the inwards-extruded area to have very sharp edges, I can add loop cuts to the sides of the shape. Then the shape will have sharp edges, however, there wll also be edges going across the whole object, which I obviously don't want.

Then I could extract the extruded faces and add edges to them. Then the extruded area will be nice and sharp and the rest of the object will stay smooth, but then the edges will cut into the middle part.

I could fix this by adding edge loops to the area that has been cut-out, but this would take me back to the previous problem - I would get those sharp edges on the smooth surface. I could also use the move tool and set it to "normals" and move the points that are not close to the sharp area away from each other, but I found that that doesn't really solve the problem either. It minimizes the sharp edges, but it's still not a very clean solution.

So how do you guys deal with this problem? How do you create sharp edges on smooth surfaces without getting those nasty edges spanning across the entire surface?

Thank you so much in advance for your advice, I've been struggling with this for so long now.


edit: I'm sorry, I wanted to post this into the modeling-forum and opened the wrong tab

Last edited by mauspat : 02 February 2018 at 09:01 PM. Reason: posted in wrong forum
  02 February 2018
You need to start with a sphere that has more density and cut your details, then throw on a subdivision (or more depending on desired tightness). A denser mesh will support finer details, thus sharper edges.

Sphere 1. (top left) is a dense sphere with shape cut (the square shape edges have been beveled inwards for visual interest)

Sphere 2. (top right) has the same density but the contour of the square shape has support edges to make the border sharp.

Sphere 3. Has the same polygon count as sphere 1, except the density is distributed in a different manner and results in tighter border
This version could benefit from a support edge and keep relatively the same polycount and have tighter contour.

Sphere 4. How tight / high are you ready to go?

Most of these require very little manipulation, everything is done through the use of smoothing groups (hard edges in maya?) and stacking subdivision modifiers on top.
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