Hi all,
I added subdivision surface to a simple extruded object. But it doesn’t round up an object by all sides and follow it’s own shape. Instead, It has some extra flat surfaces comes up at left and right side of an object. Anyone please help explain why this happen ?
Because it is trying to subdivide and smooth all the surfaces while still trying to keep the base shape. There are no new…
But the translation of surfaces that are already there… the Sides get rounded trying to round all the shapes but there are intersections from the protruding bits so it compensates for those by keeping the intersection while still smoothing the protruding bits at the same time… To sum up, that’s the way sub-d works… If you want to keep the shape and still add a subdivision surface, set it to simple instead…
See what happens when you add a Cube and put a subdivision modifier on it…you get a sphere…
What should I do to get the shape rounded up ? setting sub d to simple still has that surfaces comes up.
N-gons don’t really exist. They appear as such for modeling convenience, but they’re “implicitely triangulated”. The subdivision scheme has no clue about this, it just sees the triangles, and subdivides them as such -messily.
If you want to keep the sides completely straight, you’re going to have to retopo them so that they’re made of several quads instead of a single, large n-gon. Just roughly connect up the sides with the knife tool (K) or the connect vertex operator (J). Ultimately Blender will still try to smooth them, but you can work around that by setting down support loops or creasing the border edges (shift+E) to the max.
Subdivision does not maintain the shape.
You must configure the appropriate topology or use a remesh.
Thanks guys for yours suggestion. So I select that “n-gon” (face that connect more than 4 vertices) and go to Face>Triangulate Face and then Face>Tris to quads. This way is like an easy way to quick add some topology ?
I didn’t think of this, well if it works for you it’s all good. As a final step I would advise selecting the ngon (or the faces that used to be the ngon) and inset (I) so that the normals around the edge behave well (otherwise you’re going to get shading artifacts).
Thanks Hadriscus. I’m very noob. I don’t understand much about topology or what you guys said. I’m trying to learn.
However, add an inset has interesting result. It force the surface to be flat. In the picture compare to the other side that doesn’t has inset.
That was the idea, but perhaps I misunderstood what you were going for
Imagine a cube.
If you subdivide this object, it will become more or less a sphere.
Why? because Blender want’s to round off the object on the corner edges from one side to the other.
Now add edgeloops close to the existing edges on all sides. SubD the cube now, and you will see it keep it’s shape as much as possible, only smoothing out the small areas on the corner edges.
This works for insets as well, because you’re adding another ‘border’ for the Subdivide to work in.
This behavior works for all modeling.
And if you need so called ‘hard edges’, there’s a way to do that too. 
Happy modeling!
rob
Please refer to the video.
For the sake of accuracy, it’s not true that “n-gons don’t really exist.” The Catmull-Clark subdivision scheme absolutely subdivides n-gons as well as triangles and quads. There is a stage where geometry is triangulated, but that happens after and not before the geometry is subdivided.
Catmull-Clark subdivision creates a new vertex in the middle of a face and splits every edge, resulting in new vertices on every original edge. Those new “edge” vertices are connected to the new “face” vertex. A quad would be subdivided very differently if it were triangulated before subdivision (see below).
NOTE I sketched how the topology would change not the positions:
I also sketched an example of how Catmull-Clark subdivides an n-gon.
Forgive me for getting nerdy here, but understanding how Catmull-Clark works under the hood helps everyone be better modelers.
I forgive and thank you for this.
