Subd pinching problem

Kawe

So I decided to learn subd modeling. However I've run into a problem with pinching as seen on the image below:



I assume that it is the pole that is causing the problem and I tried to do this in two ways but I ended up getting the same pinching error.

First I tried to just bevel/extrude and just add an edge loop around the center to get a more squared look (top right image) but it caused a lot of pinching. So I browsed the forums and other sites and people seemed to suggest to just bevel the edges of interest. I tried that (bottom left) but alas the pinching is still there.

I've checked the wiki, searched the forums as well as any external links I could find. But I can't seem to find a solution.

Now I've run out of ideas and I feel really dumb cause this must be one of the most rudimentary problems out there.

Cojax

Kinda hard to tell but it looks like you have a triangle in that mesh. Avoid Triangles in sub-d.

Wokky

I'm not sure if this is the issue you're talking about, as I'm finding it a little hard to see precisely what you're talking about in your image, but one problem I see with your mesh at the moment is that you've not got any edges defining the outer curvature in your inset segments. That means that they're staying very straight-edged, while the polys behind them on the main part of the cylinder are curving around evenly, which would create pinching. The only real solution to that is to increase the number of edges.

Hopefully that actually made sense.

Kawe

Sadly I don't think I understand where you want me to put those edges.

I made another picture to show the problem:



It is all quads except for a few ngons (cylinder caps and the inside of the insets) but they shouldn't be affecting much.

Illusions

You don't have a stray vert or something there would you? I've been running into that problem on some stuff I'm doing, where I'll have deleted an edge or removed some polygons and forgot to clean them up, or accidently doubled up an edge somewhere...

I mainly ask this because your error is happening where I assume you've welded together duplicated instances of the same original piece (the inset).

vik

also stars (vertices connecting more than 4 edges) can cause pinching and you have them in your mesh

Kawe

No stray verts. I'm also guessing it is the pole (star) that is causing the pinching but I don't really know how I should get rid of it in a good way.

MoP

Wokky is correct in this case, Illusions makes a good suggestion but I don't think that's the case here.

As for what Cojax says about triangles in sub-d meshes, that's not true. Use any sort of n-gons you want, obviously quads will subdivide more "predictably", but you can easily use 5,6,7+ sided polys if you want, and triangles if you need. The main thing is what the subdivided result looks like, doesn't really matter how you construct it.

The main reason for keeping quads other than predictable subdivision results is so that you can use loop/ring selecting tools, so obviously it is a good idea to work mainly in quads, but there's no point spending time trying to get rid of tris/n-gons if the resulting subdivided mesh looks good.

Basically to fix this you will need to have more divisions running down your main cylinder piece.

The pole (star geometry) isn't helping either, since the more edges that are connected to a vertex, the more "weight" the vertex will have (retaining its original shape) when subdivided.
Similarly, the closer together verts/edges are, the more "weight" they will have when subdivided, which is why if you want a "sharp" edge, you bevel it or put loops on either side.

Cojax

Last I checked Triangles were bad. But hey wtf do I know.

Microneezia

Wouldnt this stop the pulling down on the verts?

EarthQuake

Triangles/Ngons can be bad if you're using them in detail areas to define shape. If you've got a triangle in a flat area of your mesh that isnt defining a curve or anything, its perfectly fine. I use ngons quite a bit to transition from shapes into different shapes, often you need different types of tesselation/geometry to define different types of curves etc. So ngons are really your only choice in those situations, keeping all quads can often be an excersize in futility

Cojax

EarthQuake wrote: »

Triangles/Ngons can be bad if you're using them in detail areas to define shape. If you've got a triangle in a flat area of your mesh that isnt defining a curve or anything, its perfectly fine. I use ngons quite a bit to transition from shapes into different shapes, often you need different types of tesselation/geometry to define different types of curves etc. So ngons are really your only choice in those situations, keeping all quads can often be an excersize in futility

Thankyou. Maybe I should take the time to explain it next time like EQ here. haha.

Kawe

So I tried to add more division in all manners but it barely helped. Only time it helped slightly was when I added division along the height of the cylinder but that of course also made it less round...

I also tried Microneezia's suggestion and that didn't work at all.

If anyone could be kind and show how they would do this I think it'd be really helpful I've been trying to get this right for a while now. Technically it isn't that much of an issue. I bet that if I made a normal map out of this I could prolly paint the errors away but hey.... that's not what I want to do.

Illusions

EarthQuake wrote: »

keeping all quads can often be an excersize in futility

Bah...good to know, having issues at home on a mechanical model I'm trying to do.

EarthQuake

Ok heres an example of how to do this, using NGONS lol

Like a lot of solutions to complicated mesh with sub-ds, sometimes the answer is just to throw more geometry at it! since you want to retain those curves you have, the # of sides shouldn't = the inset features, it should be more, in this case i used 3 sides per indent, then added in some padding edges around each indent, then beveled padding edges around the shape, and added edges to retain the shape etc. And then finally, remove the excess loops so you dont have sharp edgse every 3 sides. Thus creating NGONS!!! MWUAHAHAHA



also http://johnyontehspot.com/pix/shapething.obj

Kawe

Hey, thanks EQ Helps a lot.



You forgot the triangles I believe

Wokky

Was just about to post an example pic to explain myself better, but it looks like EQ has beaten me to it by 2 seconds, and 16 minutes... and 12 hours. I do plan to post it someday Kawe.