Subdivision cylinder / polygon edge extrude

[lapdog]

From a tutorial, create a subdivision cylinder, go to polygon proxy mode, select top and bottom capping faces and delete to create an open subdivision cylinder.

The polygon proxy is six sided while the subdivision surface is "12 sided", or rather two subd patches per single polygon side. When the top edges of polygon proxy (six edges) are extruded up, you see this lumpy sufrace we go from 12 subdivision edges to 6 subdivision edges on the extruded surface. This results in a rough (not smooth) surface.

I don't see anyway to create a 12 sided subdivision extrusion, but then I'm not fluent with subdivision modeling. Could anyone clue me in as how to do an extrusion with a resulting 12 subdivision edges. Hope the question is clear enough.

[drblacksnake]

You may first extrude caps, then delete them.
Anyway in Your case looks like You have keepFacesTogether OFF in extrude.

[lapdog]

Here is a picture of the subdivision behavior I'm asking about.

http://www.sambana.com/temp/subd\_edge\_extrude.jpg

1. Create subd cylinder
2. Switch to polygon proxy mode
3. Select top and bottom faces
4. Delete faces to create open cylinder
5. Select top edges on proxy
6. Select Extrude edges (notice the problems in the surface)
7. Pull the extrude upwards (again, notice the problems in the surface)
8. Picture 8 illustratates that the extrude started with six polygon proxy edges influencing 12 subd edges. After the extrude, the new surface has 6 subd eges.

By selecting subd (not poly) vertexes at level 1 and pulling and then undoing I then get the surface I want.. The next extrude will have the same problem though.

What I am asking is a) how to understand what is happening (proxy, subd interaction) on this subd cylinder and how to influence the behavior of the proxy to acheive a consistant subd surface.

By the way, keeping the top/bottom faces does not help - extruding faces has the same results. Also, "Keeping Faces Together" off does not help.

Thank-you for your reply

[joojaa]

your Polygons->Tool Options->Keep Faces Together is off turn it on!

and yes the two faces thing is to expect its becaus ethe lower part has more idetail levels than the upper! NOthing worng with the subd its just how maya tesselates them.

Alo note if you inly wrk on levell 1 then it does not matter,

[lapdog]

I think I see what you are saying. Rendering results in a smooth surface even though the panel view shows an uneven surface.

I was getting irratated by a display issue where gaps (or rough edges/surfaces) would appear during editing. See this picture of an example where moving a level 1 vertex would result in a surface gap (but not a render gap)

http://www.sambana.com/temp/subd\_edge\_extrude\_gap.jpg

Your explanation helps. I was molding a subd surface to an imageplane drawing and found it difficult to mold the surface becuase of these display issues.

I'm still a little puzzled by the phenonemon but at least know the surface is still there and behaving more or less correctly.

[joojaa]

select surface and hot 2 or 3 for a smoother diplay than hull!

[lapdog]

Yep, hitting 2 or 3 a few times results in a smoother display surface. I was feeling dumb until I tried extruding edges, smooth display, and then extrude again using the same edges. This results in an extruded polygon without a visible subd surface. I'm not making this up - see picture.

http://www.sambana.com/temp/subd_edge_extrude_missing.jpghttp://www.sambana.com/temp/subd\_edge\_extrude\_missing.jpg

And thanks!

[joojaa]

youve accidenttaly succeded in disconnecting the polycage from the history of the subd. It happens espacialy to those that dont udnesrastand what they do. You cant delete history on theese shapes for instance. (maya has a pretty general approach to stuff instead of inventing a new surfacetype alltogether use whats allready here, and the history syetem has many advantages, and few supprising side effects)

[lapdog]

Hey, Joojas, thanks so much for the help and for the explanation.

I am the first to admit that I lack experience here (especially with subD's). But in my defense, if I do edge extrudge on the cage, followed by another edge extrudge without deselecting, then okay. But if I edge extrude, smooth display, edge extruge again (same edges), then I get the disconnect you talk about. Something fishy here, unless I did something wrong.

[drblacksnake]

i guess when You smooth display, somehow subd shape gets selected too. After you do 2nd edge extrude it succeeds on polyEdges, but fails on very subd, since it is poly tool.
personally i never use those primitives and very often model lowpoly model wihout subd, and then do convert. just few adjustments then necessary. anyway theres easier later to map UVs on poly than on subd.
just get familiar with this technique and later you'll see all nuances.

[lapdog]

What you say makes good sense. Thanks again for the help.

As an addendum, one solution is to use the Subdivision | Collapse Heirarchy command to make the surface uniform. In this case using Collapse Heirarchy (level 1) moves all the level 1 vertices to level 0 and creates a uniform but more detailed surface with a more detailed polygon cage.