[x3d-public] Nurbs control points, preweighted or not ?

[Andreas Plesch]

Let's assume for now that x3dv4 is not the time to make such a change.
x3dom will revert to the uncommon behaviour of expecting preweighted
control points.

Andreas

---on the phone---

On Fri, May 22, 2020, 10:02 AM Andreas Plesch <andreasplesch at gmail.com>
wrote:

> Thanks, very interesting. The formula png does not show for me directly
> but scrolling down in
>
> https://www.web3d.org/documents/specifications/14772-1/V2.1/
>
> to section 4.16.2 shows the equation and the explanation of the variables.
>
> Just to confirm:
>
> V_i,j is  the mesh of control points, likely meaning the value of the
> controlPoint field.
>
> Note that in the formula V_i,j is multiplied by their weight w_i,j in the
> numerator, which requires that V_i,j are given not premultiplied.
>
> Is it time adopt the same formula for X3D v.4.0 ?
>
> [In theory, it is possible to think about a slower transition path by
> introducing new nodes or new fields such as controlPointL (local) for
> non-weighted controlPoints but I think a clean break is better.]
>
> -Andreas
>
> On Thu, May 21, 2020 at 10:12 PM J. Scheurich <mufti11 at web.de> wrote:
>
>> BTW: the NURBS formula in VRML97 Amd1. has a extra weight variable:
>>
>>
>> https://www.web3d.org/documents/specifications/14772-1/V2.1/Images/NURBEq.png
>>
>> w   is the weight
>>    i
>> V   is the controlpoint
>>    i
>>
>> Maybe the X3D standart should use a similar formula ?
>>
>> so long
>> MUFTI
>>
>
>
> --
> Andreas Plesch
> Waltham, MA 02453
>
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