Subdivisions produce bad solids

[Kaare Baekgaard]

I am in the process of using the first subdivision-derived object in a design.

The overall shape is good and I am pleased with it:

https://drive.google.com/file/d/0BxL3Oyph55RRRVpKRUtzeWJpZ0E/view?usp=sharing

But as it turns out, the square patches of the generic solid - which you can see in the top illustration – have been poorly programmed, and as a result, I cannot use the command 'shell solid' on the object – or on any object derived from it.

I now have to use hours to clean up the surfaces one by one and rebuild the solid patch by patch, because I need to shell it.

One problem is lots of redundant vertices. Each square patch has been loaded with 110. The sufficient amount would be 25. This may or may not be the actual root of the problem, but makes it a lot harder to get reliable results in solid operations.

I wish that you will make sure, that objects derived from subdivisions can be used with the shell solid tool.

[PVA - Admin]

What specifically would correct this in subdivision creation however? A cylinder, cube, rectangular prism or curved pipe made with subdiv for instance can be shelled without issue after converting to a solid, but a more abstract shape like the above example cannot. This seems more like a deficiency in the Shell tool, it hasn't been faced with the more unusual shapes that subdivs are able to create until this version.

[Kevin McAllister]

I have a question about the result shown. Is the top shape the subdivision object and the bottom the solid? The reason I ask is because I understood that the Subdivision tool ultimately created a mesh - so I would understand that the solid is derived from that mesh, not from the subdivision iso curves.

As an aside, the top object looks like it would be a pretty nice NURBS object. Its too bad the Subdivision object didn't create NURBS surfaces instead of a mesh...... I guess that's what you get when you use a technology designed for video games....

Generally I have some concern about how much emphasis is being put on visualization over real geometry and accuracy in a CAD program, but that's a discussion for another day.

KM

[PVA - Admin]

The last video in the Subdiv series shows you the different object types you can get out of a subdivision:

You can get Generic Solids, Meshes, NURBS Surfaces, or even 3D Polygons if you really wanted, there are different methods to get each, the Convert command doesn't do them all.

[zoomer]

^

Are these Videos new ?

There should be a special Thread to announce new Videos that I will not miss them ....

[rDesign]

^

Are these Videos new ?

There should be a special Thread to announce new Videos that I will not miss them ....

New topics get created so fast around here you might have missed it but JimW did create a special thread for it:

Subdivision Introductory Tutorials

[PVA - Admin]

You can also keep an eye on our Youtube channel, we post the public stuff there as well. You can subscribe if you want a notification when we do. (No, I don't get paid extra for subscriptions and Likes )

https://www.youtube.com/channel/UCN7uzhu-ljLJOe6a0J-fBcQ

[zoomer]

New topics get created so fast around here you might have missed it but JimW did create a special thread for it:

Subdivision Introductory Tutorials

I realized and found these by chance.

Was just surprised that I have overseen some new Videos that were released

3 long days ago

Just thought the hot phase of releasing VW 2016 stuff would be over meanwhile.

Will keep my eyes open ....

[Kaare Baekgaard]

What specifically would correct this in subdivision creation however? A cylinder, cube, rectangular prism or curved pipe made with subdiv for instance can be shelled without issue after converting to a solid, but a more abstract shape like the above example cannot. This seems more like a deficiency in the Shell tool, it hasn't been faced with the more unusual shapes that subdivs are able to create until this version.

Hi Jim

As a product designer, I have shelled complex nurbs objects before, so it can certainly be done if you are careful.

Here is what I did:

The original converted nurbs surfaces could neither be used for shelling nor as cutting tool in a section solid.

So I painstakingly position-matched every pair of connecting edges of every patch using the connect/combine tool.

After this I could use the resulting solid as a cutting tool for a section solid and I could shell that solid to a limited thickness.

If I had made the efford to reduce every patch to 25 vertices, the shell could have been made much thicker. But it would have taken me a days work to make sure that the surface of every patch were tangent to its neighbours.

What this tells me is, that when a subdivision is converted to nurbs or a nurbs-based solid, the edges of the nurbs surfaces have not been reliably position-matched. (they don't meet up)

This is a rather serious flaw in the programming, so i urge you to pass on that information to the programmer in charge of subdivisions.

Edited October 24, 2015 by Kaare Baekgaard

[Kevin McAllister]

As an aside, the top object looks like it would be a pretty nice NURBS object. Its too bad the Subdivision object didn't create NURBS surfaces instead of a mesh......

Hi Jim,

Thanks for the link. And thanks for creating another great set of tutorial videos!

I believe I'm understanding that Subdivision objects are natively meshes (ie. a mesh is being generated behind the scenes as you work with it and when you ungroup it, you get a mesh). So all of the other output types you can derive from it are conversions. In my experience, VW conversions are often not that robust as this example is showing. From a user perspective this probably means we need to bug submit as many problem objects as we can so this can be improved.

This other thread is definitely linked to this same discussion - https://techboard.vectorworks.net/ubbthreads.php?ubb=showflat&Number=215702&gonew=1#UNREAD

Kevin

[zoomer]

So I painstakingly position-matched every pair of connecting edges of every patch using the connect/combine tool.

Where is that tool ?

I wasn't able to combine any NURBS Surfaces.

Just 3d power pack > Stich and trim surfaces,

which will give me a Generic Solid only.

[rDesign]

So I painstakingly position-matched every pair of connecting edges of every patch using the connect/combine tool.

Where is that tool ?

I wasn't able to combine any NURBS Surfaces.

Just 3d power pack > Stich and trim surfaces,

which will give me a Generic Solid only.

@zoomer: here's a link to the help topic on the Connect / Combine tool, it describes Position-matching for NURBS that Kaare was describing. HTH.

Combining and Connecting Objects : Vw2015 online help

[zoomer]

Of course that helps !

Basic 2D tools was the least where I would search for such a thing.

Will look into it ....

[Kevin McAllister]

That's a cool thing to learn about the Connect / Combine tool. I wish the documentation went into a little more detail though....

KM

[zoomer]

But I'm not sure if it does what I want or if that is possible at all.

I made a simple extrude,

converted to NURBS => 6 grouped NURBS Surfaces

Know I tried to combine those N Surfaces,

or at least 5 of it.

As you can always connect Faces that touch on one edge only (?)

it stopped for me when trying to connect a third Side to a pair of Surfaces.

Maybe I'm "holding it wrong"

[Kaare Baekgaard]

Maybe I'm "holding it wrong"

I use the tool a little different in that I identify two edges by clicking one after the other.

It is a little awkward, when the edges are very close; in this case I have to drag one of the vertices of the first edge away, so I can safely identify that edge with the connect/combine tool and let its position match the second selected edge.

[zoomer]

OK,

have to try again ....

[PVA - Admin]

Gathering the above info as well as this:

https://techboard.vectorworks.net/ubbthreads.php?ubb=showflat&Number=218165#Post218165

Into a request/chat with engineering.