[x3d-public] Mantis 1392: 5.3.20 SFVec4d and MFVec4d defaultvalue (0 0 0 1) or (0 0 0 0) ?

[Michalis Kamburelis]

4D vectors in X3D don't hold quaternions. In X3D rotations are in
SF/MFRotation given as axis-angle.

W dniu wt., 15.03.2022 o 00:05 Joseph D Williams <joedwil at earthlink.net>
napisał(a):

>
>    - three-dimensional (3D) homogeneous vector
>
>
>
> For safety, default should be a legal quaternion (xyzw add to 1?) then 0 0
> 0 0 not good but generally 0 0 0 1 should be harmless as a default. I
> haven’t found all places this is used
>
> Default rotation is 0 0 1 0 (ready to roll if it gets some angle).
> Likewise, 0 0 0 1 is legal and ready to do whatever if its gets some xyz
> data.
>
> Thanks,
>
> Joe
>
>
>
> *From: *Michalis Kamburelis <michalis.kambi at gmail.com>
> *Sent: *Sunday, March 13, 2022 3:08 PM
> *To: *John Carlson <yottzumm at gmail.com>
> *Cc: *X3D Public Mailing List (x3d-public at web3d.org)
> <x3d-public at web3d.org>
> *Subject: *Re: [x3d-public] Mantis 1392: 5.3.20 SFVec4d and MFVec4d
> defaultvalue (0 0 0 1) or (0 0 0 0) ?
>
>
>
> The description of 4D vectors states their purpose: "a
>
> three-dimensional (3D) homogeneous vector".
>
>
>
> The 4D value "0 0 0 1" means "3D position at (0,0,0), when interpreted
>
> as (3D) homogeneous vector".
>
>
>
> The 4D value "0 0 0 0" would mean "invalid value, when interpreted as
>
> (3D) homogeneous vector".
>
>
>
> Let's keep the "0 0 0 1" as default. I don't see any reason to change,
>
> "0 0 0 1" makes sense. (One could also argue that "0 0 0 0" makes
>
> sense, but it is a flip a coin, they both can be argued as "better
>
> defaults". So, no reason to break compatibility.)
>
>
>
> Regards,
>
> Michalis
>
>
>
>
>
> niedz., 13 mar 2022 o 19:48 John Carlson <yottzumm at gmail.com> napisał(a):
>
> >
>
> > My guess is it has to do with a perspective transformation.
>
> >
>
> > John
>
> >
>
> > On Sun, Mar 13, 2022 at 1:35 PM Brutzman, Donald (Don) (CIV) <
> brutzman at nps.edu> wrote:
>
> >>
>
> >> Clause 5.3.20 SFVec4d and MFVec4d lists default value as (0 0 0 1)
>
> >>
>
> >>
>
> >>
>
> >> Why not (0 0 0 0) similar to other SFVec/MFVec fields?
>
> >>
>
> >>
>
> >>
>
> >>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/Part01/fieldTypes.html#SFVec4dAndMFVec4d
>
> >>
>
> >>
>
> >>
>
> >> Similarly for 5.3.21 SFVec4f and MFVec4f
>
> >>
>
> >>
>
> >>
>
> >>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/Part01/fieldTypes.html#SFVec4fAndMFVec4f
>
> >>
>
> >>
>
> >>
>
> >> Entered as
>
> >>
>
> >> Mantis 1392: 5.3.20 SFVec4d and MFVec4d default value (0 0 0 1) or (0 0
> 0 0) ?
>
> >> https://www.web3d.org/member-only/mantis/view.php?id=1392
>
> >>
>
> >>
>
> >>
>
> >> all the best, Don
>
> >>
>
> >> --
>
> >>
>
> >> Don Brutzman  Naval Postgraduate School, Code USW/Br
> brutzman at nps.edu
>
> >>
>
> >> Watkins 270,  MOVES Institute, Monterey CA 93943-5000 USA
> +1.831.656.2149
>
> >>
>
> >> X3D graphics, virtual worlds, Navy robotics https://
> faculty.nps.edu/brutzman
>
> >>
>
> >>
>
> >>
>
> >> _______________________________________________
>
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>
> >> x3d-public at web3d.org
>
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>
> >
>
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>
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>
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>
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