How to create a tensile tight surface All  1-4  5-15

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 From:  Michael Gibson
3645.5 In reply to 3645.3 
Hi nufu,

> If I make a new tent shape with the freeform curve, and
> use network, nothing happens.

Could you please post the curves for your new tent shape that you are having a problem with so we could see them?

But Plasma is right - you need to have 4 curves on the outside part, if you have just one big joined curve that could be the problem.

Basically Network needs to be made up of 2 sets of curves that cross each other like a grid.

So for example in Plasma's file, here is one set:



and here is the other set:




Network needs curves organized in this kind of grid crossing pattern for it to work.

- Michael

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 From:  Michael Gibson
3645.6 In reply to 3645.1 
Some other techniques you could also try -

See this previous post for making something with dimples in it, you may be able to adapt that for what you need:
http://moi3d.com/forum/index.php?webtag=MOI&msg=2983.1


You could also try surface control point manipulation:
http://localhost/forum/index.php?webtag=MOI&msg=863.2


Also that kind of tensile surface is also called a "minimal surface", you may be able to find some specialized tools that are focused on producing that kind of thing.

Here's a couple:
http://www.susqu.edu/brakke/evolver/evolver.html
http://www.ixcube.com/dettagli.asp?n=20


Another possibility would be an animation program that has a physics simulator in it, for example Maya has a cloth module where you can make a mesh sheet behave like cloth and actually drop it on top of some poles.


- Michael
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 From:  nufu
3645.7 
Hi guys,

Thanks for all the pointers. New to nurbs (after avoiding them in 3dsmax for 10 years), so this way of building something was a bit of a head scratcher :)

Managed to get it working and shaped quite nicely, but as you can see in the attached file it has quite a few pinching parts.

I have tried adding more curves to the cage, but it doesn't seem to help. Can the surface be relaxed somehow?


Thanks again :)
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 From:  Michael Gibson
3645.8 In reply to 3645.7 
Hi nufu, actually this project does not particularly leverage the best strengths of NURBS because you are working with a shape that is not able to be fully described by 2D profile curves.

Working with full 3D curves and wavy surfacing tends to be a more advanced area of NURBS modeling, and you also move more into the territory of what sub-d modeling is more suited for.

That's particularly the case if you have little folds and details on your surfaces. Most often those are parts of organic shapes like parts around eyes and mouths but you have a similar kind of model to that here where you kind of want some small localized folds.

So I'd say your particular project here is probably better suited for sub-d tools and not NURBS tools really.

If you had any kind of mechanical shape that you wanted to construct, that would be much more the area where you would find the NURBS tools much more suitable.


> Can the surface be relaxed somehow?

There are not currently any tools in MoI for sort of mutating or melting a shape that you have already created, that's again something more suited for polygon modeling.

It can tend to help to use fewer curves to make a more relaxed surface rather than using more though, the more curves you add tends to add more constraints and more "pressure" applying to the surface which tends to make undulations unless all the curves are positioned in a really good shape.

It would also help if your curves were closer to touching each other, there are many areas where the different curves are fairly far apart from each other, that tends to cause Netowork to make that kind of patchy type result. For example there is quite a large gap between these 2 ones:




Those kinds of large gaps kind of reduce the accuracy and smoothness of the final result, there will be a kind of fight between the different directions in those areas, producing a sort of fault line.

I don't really think you're going to get a nice result with Network on this case though, you've just got too many irregularities in it, too many areas with really sharp bends, too much variation between different shapes...

NURBS surfacing tools tend to be better suited for broader smoother sheets that don't have small localized bumps or folds in them.

- Michael
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 From:  BurrMan
3645.9 In reply to 3645.8 
I've been trying to see a way to do this. It just seemed like it should. Here I used a revolve tent object, then placed 4 at different pole angles, and booleaned to a larger curved surface. Then I could fillet between them to finish the "cloth". If it is close at all, we can look at best practices. If not, just another failed attempt.. :o

EDITED: 19 Jun 2012 by BURRMAN

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 From:  Michael Gibson
3645.10 In reply to 3645.9 
Hi Burr, that is a good way to do it.

The potential difficulty might be in getting a nice blend shape between them, a fillet with a circular cross-section may give a kind of "machined" look to the blended area. Using a G2 blend shape instead of circular shape could help with that. It may have some difficulty getting a nice shape in the shared corner region between 3 of the shapes where the blends come together.

Then if you want to produce a kind of pointy outline around the outer edge of the shape you could do that by trimming away some of the outside area by a profile curve from the top rather than trying to incorporate an outline like this directly into the surface construction:




It tends to be difficult to surface something with such irregularity or localized small tight bends in it directly, instead building a more simple smooth larger surface like you are showing and then trimming it is usually better.

- Michael
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 From:  BurrMan
3645.11 In reply to 3645.10 
Hi Michael,
Yes I noticed this. The circular fillet didnt seem like a "perfect finish". The G2 looked better, but produced some folds at intersection areas. Too much adjusting to try and get perfect!!!

I was wondering if the "multi edge Blend" may work here when we get that tool. I had started with a blend idea but had to abandon it. The ability to blend between "3 or 4 cones" would probably do this easy...

Thanks for looking.
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 From:  Michael Gibson
3645.12 In reply to 3645.11 
Hi Burr,

> I was wondering if the "multi edge Blend" may work
> here when we get that tool.

Yeah often that is called an "N-sided patch" that fits a surface through some potentially irregular boundary edges while maintaining tangency to existing surfaces there. That kind of tool would help to fill in the areas where several blends are coming together.


You would still use the regular Blend command to build most of the connections, but the N-sided patch where the various blends collide with one another.


The Blend command handling multiple edges is slightly different - it's still a 2-sided thing but it means making it possible to have a chain of various different edges for each side of the blend rather than just 1 single edge on each side.

- Michael
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 From:  BurrMan
3645.13 In reply to 3645.12 
SO here is a blend attempt.Between each revolve is a blend that works well, but your left with that middle hole. Is this a part we cant do without "N-Patch" or is there a way to fill this. I was thinking even of putting in a tiny little surface in the top center and using blend on the four edges again, then just having the little tiny thing at top be a bit rough (Or even fill it with a new revolve tent, like a vent top).

Anyway, seemd close except for this last part which it seems like you were talking about already.

EDITED: 19 Jun 2012 by BURRMAN

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 From:  Michael Gibson
3645.14 In reply to 3645.13 
Hi Burr, yeah it is that center part that is the problem. Just a regular Blend is not quite good enough for that area, because Blend makes a smooth connection between 2 different sides, but in that area you want a smooth connection between 4 sides, not just 2.

You can fill the hole with something like Network or Sweep, but it will have a crease there instead of it being a smooth fill.

If you can make the hole to be a pretty small size then the crease may become difficult to see though.

But yes, filling in holes like that with a smooth surface is what an N-Sided patch tool would be used for, there is not really another tool that does the exact same job.

- Michael
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 From:  BurrMan
3645.15 In reply to 3645.14 
Got it! Thanks.
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