[x3d-public] X3D 4.0 specification problem: TextureProjectorparallel.fieldOfView

[John Carlson]

I have no issue with SFVec4f.  My only concern is system which require
field names like x:,  y:, z:,  … prior to a number.  That would seem
strange.  In that case, MFFloat might be better, or an interval field type,
which might not participate in many vital events.  Konstantin might be a
good source of information.

Food for thought.

John

On Fri, Dec 13, 2024 at 3:15 PM Brutzman, Donald (Don) (CIV) via x3d-public
<x3d-public at web3d.org> wrote:

> Excellent question, thanks for asking Holger.
>
> This issue has been carefully tracked and regularly revisited since July
> 2022.
>
>    - Mantis 1398: OrthoViewpoint fieldOfView type needs to be SFVec4f,
>    not MFFloat
>    - https://mantis.web3d.org/view.php?id=1398
>    - Mantis 1468: must SFVec4f/SFVec4d fields be homogeneous?
>    - https://mantis.web3d.org/view.php?id=1468
>
> The X3D Working Group was unable to reach consensus on this issue prior to
> conclusion of version 4.0, unfortunately.  Dick Puk and I took a close look
> at this recently too. Here is a synopsis of the Mantis issues.
>
> I advocate use of SFVec4f for all parallel fieldOfView values because it
> is the strictest appropriate datatype that can validate content. Retaining
> the legacy MFFloat type definition for fieldOfView allows 3d models
> (produced by humans or tools) to define arrays of illegal length, making
> failures mysterious.  Conceptual consistency is important too.
>
> Reviewing the Mantis issues, additional concerns included:
>
>    - *Incompatibility with prior X3D implementations.*  Since a 4-tuple
>    content value is a valid MFFloat array, I'm not seeing any backwards
>    incompatibility if a prior X3D 3.3 implementation encounters the four
>    values of a SFVec4f array.  There are no representation problems since
>    value syntax is compatible for our various encodings as well.
>
> - *SFVec4f fields are actually not homogenous coordinates.*  The spec
>    uses the word "homogenous" when referring to
>    -  X3D4 Architecture, Clause 5 Field type reference, 5.3.20 SFVec4d
>       and MFVec4d
>       -
>       https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/fieldTypes.html#SFVec4dAndMFVec4d
>       - "The SFVec4f field or event specifies a three-dimensional (3D)
>       homogeneous vector." (and similarly for SFVec4d, SFVec4f and MFVec4f).
>       - However none of these fields are mathematically homogeneous, see
>       - https://en.wikipedia.org/wiki/Homogeneous_coordinates
>       -
>       https://en.wikipedia.org/wiki/Homogeneous_coordinates#/media/File:RationalBezier2D.svg
>       - Of related note is that ClipPlane 4-tuple "plane" field is also
>       SFVec4f.
>       -
>       https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/rendering.html#ClipPlane
>
> All review welcome, hopefully I have correctly synopsized all concerns.
>
> I think it would be beneficial to resolve this issue by reaching consensus
> and applying remedies as follow.
>
>    - Omitting the over-strict word "homogenous" from the four SF/MF Vec
>    4f/4d definitions in future X3D 4.1 prose,
>    - Updating future X3D 4.1 prose to use SFVec4f for
>    TextureProjectorParallel fieldOfView,
>    - Using SFVec4f in X3D 4.0 DTD, Schema, X3DUOM validation and X3D
>    Tooltips, since that type strictly confirms fieldOfView correctness with no
>    backwards compatibility problems.
>
> Is consensus now possible?  Thanks for all careful consideration.
>
> 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
>
>
>
> ------------------------------
> *From:* Holger Seelig <holger.seelig at yahoo.de>
> *Sent:* Friday, December 13, 2024 11:29 AM
> *To:* X3D <x3d-public at web3d.org>
> *Cc:* Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>;
> khyoo at chungbuk.ac.kr <khyoo at chungbuk.ac.kr>; Myeong Won Lee <
> myeongwonlee at gmail.com>
> *Subject:* Re: [x3d-public] X3D 4.0 specification problem: upVector field
> for TextureProjector, TextureProjectorParallel
>
> I just realised that TextureProjectorparallel.fieldOfView is of type
> SFVec4f, but OrthoViewpoint.fieldOfView is of type MFFloat.
>
> Which of the two is better?
>
> OrthoViewpoint is definitely older.
>
> I think of SFVec4f as a mathematical 4d vector.
>
>
> https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/textureProjection.html#TextureProjectorParallel
>
> https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/navigation.html#OrthoViewpoint
>
> Best regards,
> Holger
>
> --
> Holger Seelig
> Leipzig, Germany
>
> holger.seelig at yahoo.de
> https://create3000.github.io/x_ite/
>
> Am 08.12.2024 um 05:21 schrieb Brutzman, Donald (Don) (CIV) via x3d-public
> <x3d-public at web3d.org>:
>
> However
>
>
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