Wrong G2Blend result on Twisted Surfaces

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 From:  mkdm
7869.1 
Hi Michael and all,

I played a bit with the twist deformation tool and control point editing both in Rhino and in Moi.

After some tests i tried to do a G2 blend, first in Rhino then in Moi also, but with wrong results.

The attached .3dm is the file that i exported from Rhino to Moi, and the images illustrate
the steps i followed to select the edges for the blend.

After the G2, or tangency also, blend operation, all i got is a joined surface and not a closed solid.


What am I doing wrong ?

Nice day and thank's,

Marco.

-----POST ADDED------
After checking what i wrote, i realized that i made a mistake.

The tangency surface blend works correctly.

But the G2 blend doesn't work.

Why ?

I can not understand what's wrong in the object's topology.

Marco.

EDITED: 2 Mar 2016 by MKDM


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 From:  futagoza (STEFAN)
7869.2 
Hi Marco,

i don't know what causes this, but was able to generate a complete solid.
What i did was to create a G2 blend in MoI, then used the blended parts
and added at the end planar surfaces. after that i took the six surfaces
from the blend into Rhino OS X trial, created there a solid and imported
the solid back into MoI and booled all 3 three parts together. Attached
is a picture of the part which is now a solid in MoI.

Hope this works for you too.

Regards
Stefan


https://www.behance.net/futagoza

EDITED: 30 Oct 2016 by STEFAN

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 From:  Michael Gibson
7869.3 In reply to 7869.1 
Hi Marco, it's difficult in general to do G2 blends on things that have sharp corners in them. What happens is the blend sees the sharp corners and then will build a blend between each separate pairs of edges, and the G2 option means to make the blend match the curvature of each surface and like in your case here each surface has a different kind of curvature and so the different blend pieces are matching different things and so won't necessarily meet up with their neighboring blend piece.

So it's basically just something that goes along with trying to blend with sharp corners, especially with doing G2 blends.



I've attached a solid result - the steps I did for that were to first trim the each blend surface with it's neighbor to cut away any overlapping portions. To do that use Edit > Separate to break the blend into individual surfaces, then select a pair of surfaces and run Edit > Trim and at the prompt that says to select cutting objects just right click or push the "Done" button to go into mutual trim mode where the surfaces will trim each other, then at the next prompt that says to select which pieces to discard, switch the mode to "Keep" and then click on the large surface pieces. That will discard the overlap pieces and get the edges closer to each other.

Then in order to join things into a solid I had to scale the object down by 1/10 in size and then do the join.

- Michael

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 From:  mkdm
7869.4 In reply to 7869.3 
Hi Michael,

Thank you very much for your very professional help!

In particular for the first part of your answer and the final phrase
"So it's basically just something that goes along with trying to blend with sharp corners, especially with doing G2 blends.".

Now it's all more clear.

I followed your instructions and all works correctly.

I suppose that the downscaling was necessary because of something about the tolerance, but i don't understand why.

My current Moi settings use millimeter as unit system, and "1.000" as decimal display.

Anyway, thanks again.

This will help me in Rhino too :)

Nice night,

Marco.
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 From:  mkdm
7869.5 In reply to 7869.2 
Hi futagoza (STEFAN),

first of all i wish to thank you for your help.

Unfortunately i was not able to get a correct result following your method,
'cause i haven't passed the first step, where you say
"What i did was to create a G2 blend in Moi, then used the blended parts
and added at the end planar surfaces.".

I did the G2 blend, but the resulting joined surface not have closed planar loops of edges, and then the Planar command did not work.

Perhaps i misunderstood your answer ?

But thanks anyway.

Marco.
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 From:  Michael Gibson
7869.6 In reply to 7869.4 
Hi Marco,

> I suppose that the downscaling was necessary because of something about the tolerance,
> but i don't understand why.

Yes, that's correct. The problem was that the different blend surfaces were not fully crossing each other - in some places they would cross each other and in other areas they were a bit apart from one another. The trimming was about trying to get rid of the crossing each other areas. The "too far apart" areas were still out of join tolerance which is 0.005 units. By scaling it down the apart areas were then under 0.005 units apart from one another and so would join. It's possible that just the scaling down alone would do it, maybe the trimming was not needed after all.

This type of blend is a fairly difficult thing, it's possible to do something like force the surfaces to touch by altering the last row of control points so the pieces would touch but at the same time that breaks the continuity right at that same spot too.

Another thing I've thought about trying is to extend the blend surfaces sideways and then I might be able to intersect them better with each other. Someday I'd like to give that method a try.

- Michael
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 From:  mkdm
7869.7 In reply to 7869.6 
Hi Michael,

"...It's possible that just the scaling down alone would do it, maybe the trimming was not needed after all."

You're right ! (obviously.....)

I tried your suggestion and it works :
1) scale all to 0.1
2) create the G2 blend
3) join all and...

voila ! The piece is a solid!

The last part of your answer remain obscure for me...
"Another thing I've thought about trying is to extend the blend surfaces sideways and then I might be able to intersect them better with each other."

I tried to do a "scale 1D" on each single blended surface, but i think i misunderstood your thought.

But now it's not so important.

Thank you very much !

Marco.
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 From:  Michael Gibson
7869.8 In reply to 7869.7 
Hi Marco,

> > "Another thing I've thought about trying is to extend the blend surfaces sideways and
> > then I might be able to intersect them better with each other."

> I tried to do a "scale 1D" on each single blended surface, but i think i misunderstood
> your thought.

Yeah I'm talking about a different kind of extension, one that keeps the current surface shape as it is and iit just grows outwarrd from there. That kind of extension can go a little crazy if the surface is very bendy though.

- MIchael
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 From:  futagoza (STEFAN)
7869.9 In reply to 7869.8 
Hi Marco,

no, you understood right...but the planar command worked for me, as you can see.

Regards
Stefan
https://www.behance.net/futagoza
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 From:  Mauro (M-DYNAMICS)
7869.10 
An alternative idea:

Do the Blend between two edges




select yellow edges,copy them and paste using same snap point (end-middle)



Extract isocurve from blended surface,snapping in the middle



delete blended surface,select three curves and two edges and do Network



repeat same operation with second set of edges :Blend surface-extract middle isocurve ,copy last yellow curve from Blend and copy first curve from Network.
Now do the second Network surface



Now join one by one all four surfaces ,then join with the rest and you'll obtain a solid



If you want to simulate better the Blend behavior you need to extract more curves:turn on points of blended surface




Extract isocurves snapping on the points



M

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 From:  mkdm
7869.11 In reply to 7869.10 
Hi Mauro,

Thank you very much for your effort and your suggestions.

It's a very smart method to operate, although it seems a bit complex.

But, evidently, to achieve a good result there's need to work hard :)

I will try it as soon as possible.

Thanks again,

Marco.
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