Problem modelling this fan shaped vase

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 From:  duke
2199.1 
Here I am again! It's not your average profile-and-lathe vase:

http://www.baccarat.com/en/home-decoration/decoration/vases/GINGKO-VASE/product/GINGKO-VASE-CLEAR-CRYSTAL-GRAND-.htm



http://www.dukecg.net/GinkoVase_01.3dm

I sketched out the curves and everything is in the right spot I think, so I selected a closed set of curves and did a network on them. My problem is 2 fold:

a) I have no control over how it interpolates it. You can see a weird lump happening on the corners in the top view.

b) I can't thicken the thing, via outline or extrude (although I know extrude is just directional, not along normals).

I suspect i'm just coming at this from the wrong direction, as though i'm poly modelling it. Any input is appreciated :)
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 From:  Michael Gibson
2199.2 In reply to 2199.1 
Hi Duke - one thing that's kind of odd in there is you've got one long joined curve that sort of looks like it has branches in it.

A single joined curve is more intended to be a single closed loop that has segments that touch each other one at a time and only end-to-end.

That's actually what you'll have there anyway, but to have a kind of branching-like set of curves joined into one there will be some doubled-back sections.

That's going to cause all kinds of problems if you attempt to use that curve for various tasks... But you must have done the existing surfaces more piece-by-piece than that already.

re: Bulge - the deal with that is that all NURBS surface are made up of a 4-sided patches. If you have a 3-sided thing, that is actually a 4-sided patch with one edge compressed down to a degenerate point.

Which edge is treated as the collapsed one can make for some different shaping with some kinds of surface constructions.

You may want to use a sweep instead of Network when you have a 3 sided piece like that, since that will let you more explicitly control which side is the degenerate one, that is for those 3 sided pieces, select the bottom edge as the sweep profile, and then the 2 longer edges that meet in a point as the rails, and that should give you a much more consistent shaping.


re: thickening - yeah extrude is a one-directional thing, for thickening along a normal, you would normally use Shell instead.

However, MoI's Shell function can not properly handle cases where the various pieces start to self-intersect, like you will have in the fairly sharp corner regions here. The thickening of this piece will need to be done in a more surface-by-surface method. I'll see if I can give you an example.

- Michael
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 From:  Michael Gibson
2199.3 In reply to 2199.1 
Hi Duke, I've attached a finished up version, which tries to show some steps unfortunately the last clean-up part is a bit detailed and hard to describe shortly, but I'll try...

With these kinds of shapes you tend to have to use the more advanced parts of the toolset with stuff like some "low-level" tools like individual surfacing and surface trimming...

Here is the sequence that I used, except there are several trimming steps for that last stage:



But what I did is start with some of the "high level" solid modeling tools to kind of get a jumpstart.

First of all, let me show you this corner in the finished result:



Notice how the original surface had 1 common vertex on the outside, but this final result has a kind of "diverging vertex" where there are 2 points on the final result with an edge between them - that kind of diverging corner situation is not handled by MoI's Shell tool automatically, it is because of this part of the shape that you can't just do a shell of the whole thing and just be all done. Not with MoI's sheller anyway, there are more advanced shell tools in other NURBS programs that could probably do it though.

So just one simple use of Shell is not going to cut it.

What I did was to build those 3-sided corners with sweeps with the bottom line as the profile curve, and the 2 long upwards edges as rails.

Then I used Edit/Separate to break everything into individual surfaces.

Then I selected all those surfaces, and use Shell to thicken each individual surface into a solid. This does not handle the inter-connections between the pieces all fully properly but it does get quite a few pieces in place. Then I used boolean union on all those pieces to fuse them all together into one solid. You can see that the base part looks all fine but there are some kind of excess corner pieces.

Then I used Edit/Separate to break this into individual surfaces again, deleted those little slivery excess parts in the corners, drew a line across here:



To trim the excess part of that yellow surface there off, then I built a kind of cover sheet over the top using Network with the 4 outside edges:



So then there is kind of a cap on top and it is actually intersecting the inner 4 surfaces, so the top cap and those inner 4 surfaces can all be trimmed to one another. Here I have hidden all the other surfaces and have just the 4 inner surfaces and the top cap visible.



To trim, those all get selected, then run Edit/Trim, right-click at the select cutting objects prompt since all objects will cut each other.

Then you pick which parts to discard or keep. In this case there are some pretty thin pieces of those side-walls to get rid of, the pieces to keep are bigger, so it is easier to switch the mode to Keep and pick the 5 pieces to keep, which looks like this:



Then join all the pieces together, that's how I got that final result.

Hope this helps, like I mentioned to do these kinds of shapes that are not very mechanical you're going to be dealing with a more advanced part of the toolset that is also harder to learn.

- Michael

EDITED: 1 Dec 2008 by MICHAEL GIBSON


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 From:  duke
2199.4 In reply to 2199.3 
Thanks for the detailed reply Michael, i'll go through it in a bit :)
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 From:  duke
2199.5 In reply to 2199.4 
I ended up doing this a bit differently. I did sweeps for the corners as per your suggestion, but then I custom made the inside using a copy of the main side, then doing blends between the two to connect it, then again around the lip to connect everything up. I then selected all and did a join (probably not a good way to do it, but I deleted everything else anyway). I ran into another problem though, with good ol' fillet. Try filleting the shown edges and look for the magical disappearing object!



http://www.dukecg.net/GinkoVase_02.3dm
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 From:  Michael Gibson
2199.6 In reply to 2199.5 
Hi Duke - the only thing to keep in mind is if you want an object with a uniform "wall thickness", then usually making a copy of an object won't produce that, you need to use Offset or Shell generally to have a result with a uniform same thickness everywhere.

But if you don't need uniform thickness, then something like what you are describing should be fine.

It looks like the problem with your model for filleting is that you've got a duplicated surface in there, I mean there is one surface that is actually 2 surfaces stacked up on top of each other, it is one of the interior ones. If you use Edit/Separate to break this model into individual surfaces, and then drag the interior pieces you'll find the one that is duplicated because it will leave its duplicate behind when you drag. And when you select it you'll get a kind of "speckly" looking selection which happens when there are 2 objects exactly coincident with each other, with one selected and one not.


Once you eliminate that duplicated surface and rejoin the other pieces up then you'll have a solid and those edges that you were looking at should Fillet fine then:




You'll probably have some problems filleting the upper outside edges though, with the upper cap surface made up of multiple pieces like this:



I don't know if you'll want to fillet that upper outside edge, but you'll probably need to make that one broader surface with a hole trimmed in the middle of it, to make that filletable rather than have it made up of 4 fragments.

- Michael

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 From:  duke
2199.7 In reply to 2199.6 
nah I didn't want uniform thickness or I would have done it the way you suggested. I just referred to the photo to get my thickness. Thanks for the tips on the fillet - i'll try to make that top a single piece.
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