[x3d-public] Problem constructing Mobius strip by extrusion of rectangular cross-section

[Anthony Judge]

Hi Vince

Thanks for the interest.

I could easily  share screen shots but the matter is so simple that
sharing the Extrusion of a 2-twist 360 orientation along the spine,
with the Extrusion of a 1-twist 180 orientation might be simplest? It
is the latter which fails and the former which is correct, but not
what I want.

My thought is the difficulty is the manner in which the Extrusion
relates the orientation to the spine. For the 180 degree case, what is
effectively required is that the spine (or a "fake spine") follow the
center of the rotating rectangular cross-section. Of course it does
not. It follows one edge. So 360 connects up but 180 ends up offset.

Of course I may have messed up with the parameters of the Extrusion

Do you need the screen shots?

Tony

On 28/08/2023, vmarchetti at kshell.com <vmarchetti at kshell.com> wrote:
> Tony
>
> This sounds like an interesting project for the X3D community to help with.
>
> As a proof of concept, this X-ITE rendering shows it is possible to render
> Mobius-like geometry in X3D:
> https://spri-open-resources.s3.us-east-2.amazonaws.com/trimobius/index.html
>
>
> The X3D file that this page is rendering may be retrieved at
> https://spri-open-resources.s3.us-east-2.amazonaws.com/trimobius/mobius.x3d
>
> If you can share screenshots or webpages with your not-satisfactory results,
> that may give us some hint as to what's going on, and also sharing code may
> also help us.
>
> Vince Marchettti
> Web3D Consortium
>
>
>
>> On Aug 28, 2023, at 1:38 AM, Anthony Judge <anthony.judge at gmail.com>
>> wrote:
>>
>> I have a working model of a Mobius strip, but it uses Indexed Faceset
>> which I cannot manipulate as I had hoped to do. Basically I want to
>> extend the edges of the strip, possibly dynamically.
>>
>> So as an alternative I extruded a thin rectangular cross-section along
>> a circular spine, but modifying the orientation of each element along
>> the spine through 180 degrees.
>>
>> This gives a correct result, except that the ends do not meet
>> correctly -- the end is offset because it is rotated around the spine.
>> This is apparent if I change the orientation through 360 degrees, when
>> the ends do connect correctly -- but I have two twists in the strip,
>> which is not what I need for a Mobius strip
>>
>> I can provide snippets of this simple issue and I can understand how
>> the issue is created by using the spine/orientation combination with
>> the extrusion.
>>
>> Any comments/help?
>>
>> Tony
>>
>> --
>> Anthony Judge
>> <anthony.judge at gmail.com>
>> www.laetusinpraesens.org
>>
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>
>


-- 
Anthony Judge
<anthony.judge at gmail.com>
www.laetusinpraesens.org
https://en.wikipedia.org/wiki/Anthony_Judge