Loft leaves open hole

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 From:  nycL45
2157.1 
I have used splines to make the bowl of a cooking spoon. When I loft it, there is small open hole where the last spline is located. How do I close that hole? When I extrude the bowl, the hole remains.

I have played with different Loft Styles and Profile combinations. And, I have tried checking/unchecking the "Closed" box. BTW, when I tried a search here, there were 515 returns.

Leonard
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 From:  Michael Gibson
2157.2 In reply to 2157.1 
Hi Leonard, can you please post a .3dm model file that has your curves and loft result in it? That would help to understand what your hole looks like.

The way the "closed" option works is like the following. Say you have these 4 curves that you are lofting:



When you do a normal loft that is not closed, it will produce this kind of a result, where the surface starts on one profile and ends on the last profile:



Using the closed option will make it pass through all profile in a "loop" type fashion, producing this result:




As far as closing off the holes at the end, that can need different strategies depending on how your shapes are set up. The easiest is if your end is planar, you can cap planar holes by selecting the object and using Construct / Planar .

- Michael

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 From:  nycL45
2157.3 In reply to 2157.2 
Hi Michael,

This is unfinished business.

Attached is the implement with the bowl hole.

Leonard
Image Attachments:
Size: 299.3 KB, Downloaded: 90 times, Dimensions: 1680x1050px
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 From:  Michael Gibson
2157.4 In reply to 2157.3 
Hi Leonard, just got your e-mail and replied, sorry I didn't look close enough to notice the hole in your new post here, I just thought that was a "Work in progress" update at first!

It can be hard to do a bowl with a kind of "topographic" style arrangement like you've got there, normally I would think more of doing vertical profiles for it (similar to what I posted earlier in this thread) instead.

One way to close off what you have in this case is to select that innermost little profile and run Construct/Planar to build a planar surface from its outline. Then zoom in until you can select that little planar surface, then select it and your larger one, and run Edit/Join and then you will have sealed off that little hole. It looks like you may have already thickened that surface into a solid with some "side walls" in it, if so then you want to delete the little side wall pieces so that you can instead join the small end cap to the bottom, the small caps will not join to the other pieces unless their edges are open and not attached to an existing surface which is why you want to delete the small vertical side wall part.


If you do want to do profiles in that direction as you have here, it can sometimes be a good idea to try and build your shape in a couple of pieces (each of which is more simplified and uses fewer profiles) and rely on filleting to smooth it out, rather than trying to build everything all in just one single surface command like Loft or Sweep.

The more profiles you add to a Loft will tend to "over constrain" it and tends to introduce undulations and wiggles in the surface unless you have things placed at very optimal locations.

Here is a method to illustrate - instead of trying to make a whole bowl in one go, I just focus first on the side parts, and intentionally let the bottom come to a sharp drop:



Now I draw some new profiles and use them to sweep a separate surface for the rounded bottom portion of the bowl:



Now these surfaces can be trimmed to one another and the excess parts discarded, then use Edit/Join to glue them together and then fillet the common edge:



The 3DM model for the above images is attached here as Bowl_filleted_bottom.zip .


The benefit to this approach is that you get to focus more on some individual elements of the shape rather than having to do the whole thing all in one go, then let fillet do some of the work to fill in a rounded part to connect things up.

Hope this helps!

- Michael

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 From:  nycL45
2157.5 In reply to 2157.4 
Thanks Michael. That is a good tutorial and I will do both methods.

Coming from a poly background, I am guilty of using the poly approach to Moi3D lofts and was wondering if the hole in the mesh and your three-step process are typical with nurbs modeling? Also, my spline profiles included subtle variations from top to bottom to influence the final form and your three splines are smooth and very similar. Is that the recommended approach, i.e., try to keep the number of splines to a minimum and add subtlety to the mesh in post (using a poly app, displacement, etc.)? I know from threads that Moi3D is not for faces but should even the most subtle surface (organic) modulation be avoided? Is it KISS, "Keep It Smooth, Stupid"? :) (Kidding around.)

Leonard

Edit: smiley face and note added for clarification.

EDITED: 3 Mar 2009 by NYCL45

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 From:  Michael Gibson
2157.6 In reply to 2157.5 
Hi Leonard,

> Is that the recommended approach, i.e., try to keep
> the number of splines to a minimum and add subtlety
> to the mesh in post (using a poly app, displacement, etc.)?

Yup, usually this is the best way to go - in general it is hard to do small fine detailed bumps in NURBS modeling.

This is sort of because the NURBS modeling workflow is focused on drawing profile curves to generate surfaces. This is kind of mis-match for fine localized details because something that has a bunch of raised areas in it for example is difficult to define clearly just by profile curves.

Like for instance a human face - even though you can draw a profile curve for a side silhouette for example, that profile does not define a very large area of the shape, as soon as you move even a slight distance away from the shape changes a lot from that profile. The profile in that case is more of a "single instant" capture of the shape and not a something that actually "drives" the shape.

Things like that where a single profile curve does not capture a somewhat extended part of the model are just not good to do with a profile-driven method. Instead those kinds of things work better to do in a sub-d or displacement app since those methods of working are better for changing just a localized area of the shape rather than a broad cross-section of it...

So I guess you may ask "why use NURBS modeling at all" ? :) The good part of NURBS modeling is there are also a lot of shapes that are well defined by profile curves and can come together very quickly when using a profile-driven workflow, often times man-made mechanical or industrial type shapes fall into this category.


> I know from threads that Moi3D is not for faces but should even
> the most subtle surface (organic) modulation be avoided?

Well, I guess it depends on what you mean by subtle... :)

It depends on the specific situation - there are circumstances where you can add subtle details like bulging or depressions if they are happening across a somewhat broader area. For an example check out the Pod tutorial:
http://moi3d.com/1.0/docs/tutorials.htm - the adjustments to the legs are pretty much like this.

Details that are need to be more localized to a smaller area of the model tend to be the ones that don't work as well.


But yeah in general the KISS idea is on the right track! :) It just tends to work best with NURBS when you follow that kind of method of building somewhat more simple pieces and then trimming and filleting them together.

- Michael
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 From:  nycL45
2157.7 In reply to 2157.6 
That was a good explanation and the Pod tutorial was helpful, Michael.

Next, I will try capping the hole and your three-part method.

Thanks again.

Leonard
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