[x3d-public] X3D 4.0 specification problem: OrthoViewpoint.fieldOfView
Michalis Kamburelis
michalis.kambi at gmail.com
Fri Dec 20 08:18:24 PST 2024
Thank you Don!
I didn't catch earlier that the change (of fieldOfView type) is only
proposed now, not yet done. Hence my wording ("1 - revert this change",
which should be then "1 - leave the spec as it is"). Ok, it's all good
then, let's keep talking:)
I recognize this OrthoViewpoint.fieldOfView is inconsistent, but I see no
easy way out for now.
Regards,
Michalis
pt., 20 gru 2024, 17:02 użytkownik Brutzman, Donald (Don) (CIV) <
brutzman at nps.edu> napisał:
> [changed subject line to match topic]
>
> To be clear, no changes have been applied anywhere for changing the type
> from (MFFloat of length 4) to SFVec4f. Further we are not near consensus.
> Here are the fields:
>
> - ClipPlane plane is *SFVec4f*
> - TextureProjectorParallel fieldOfView is *SFVec4f*
> - OrthoViewpoint fieldOfView is *MFFloat of length 4* (which is not
> easily validatable, and inconsistent)
>
> Until our email discussion this past week, I had mistakenly thought that
> such a potential v4.1 change did not break backwards compatibility with any
> of our existing file encodings... Thanks for patiently helping to achieve
> that realization. The cause of this misunderstanding was due to omissions
> in the v3.3 ClassicVRML specification regarding use of brackets - they are
> not applied to SF types. We are now working on corrections with rationale
> and preliminary changes in the draft v4.0 ClassicVRML specification.
>
> - Mantis 1484: ClassicVRML field reference does not include proper
> SFVec examples
> - https://mantis.web3d.org/view.php?id=1484
>
> - X3D Classic VRML encoding version 4.0 draft, clause 5 Encoding of
> fields
> -
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19776-2v4.0-WD1/Part02/EncodingOfFields.html
> - One of several suggested revisions in progress:
> - "Single-valued fields (SF types) are written as a list of one or
> more values, depending on the type. (For example, an SFVec3f type is a
> three-tuple array of three float values.) No square brackets ("[ ]") are
> written."
>
> The best time to fix this inconsistent typing would have been when we
> approved a number of corrections in X3D 4.0. We did not reach agreement
> during that long effort.
>
> The strict typing of X3D is very powerful. Given our long efforts to
> achieve a unified object model, there are very few inconsistencies...
> offhand, am unable to think of any others. Validatable fast parsing is
> also very powerful. We won't be breaking that by engineering hacks into
> the field grammars.
>
> This keeps us unchanged at your option (1) below, Michalis. Due to being
> unable to reconcile a change for an early X3D design choice (in version
> 3.2) for OrthoViewpoint fieldOfView: we live with this inconsistency,
> allowing the presence of undetected invalid content in models. Example
> errors:
>
> <OrthoViewpoint DEF='Error1' fieldOfView='0'/>
> <OrthoViewpoint DEF='Error2' fieldOfView='0 0'/>
> <OrthoViewpoint DEF='Error3' fieldOfView='0 0 1'/>
> <OrthoViewpoint DEF='Error5' fieldOfView='0 0 1 1 1'/>
>
> As before during X3D 4.0 review, I don't recommend this state of affairs
> but can live with it.
>
> If there is willingness to change, the only remaining path forward is
>
> - Agreeing to fix this type inconsistency in X3D 4.1, OrthoViewpoint
> fieldOfView becomes SFVec3f
> - VRML parsers support either form of encoding (perhaps adapting
> Doug's suggestion). For example
> - DEF Original3.2 OrthoViewpoint { fieldOfView [1, -1, 1, 1] } #
> with square brackets
> - DEF Revised4.x OrthoViewpoint { fieldOfView -1 -1 1 1 } #
> without square brackets
>
> Onward we go. Happy Holidays everyone.
>
>
> 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:* Michalis Kamburelis <michalis.kambi at gmail.com>
> *Sent:* Friday, December 20, 2024 12:34 AM
> *To:* Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>
> *Cc:* GPU Group <gpugroup at gmail.com>; Extensible 3D (X3D) Graphics public
> discussion <x3d-public at web3d.org>; 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:
> TextureProjectorparallel.fieldOfView
>
> Personally, I like Doug solution with "fieldOfView4f SFVec4f" .
>
> As for DRY -- indeed it would be perfect to not have 2 fields doing
> the same thing, but in the current situation we don't have a luxury of
> doing a perfect solution :) Next steps, in my order of preference:
>
> 1. Simply revert this change. Make OrthoViewport.fieldOfView again MFFloat.
>
> The problems introduced by this change are not worth the gain,
> IMHO. Changing OrthoViewport.fieldOfView to SFVec4f is a consistency
> improvement for a single field in single node. It's not worth now
> checking / changing encodings and APIs to make sure that everything
> that gets/sets MFFloat can also get/set SFVec4f.
>
> 2. Add 2nd field with SFVec4f, like "fieldOfView4f". Keep
> "fieldOfView" as MFFloat.
>
> I propose a modified version of Doug suggestion (different
> fallback order, because it seems more natural to check MFFloat count):
>
> - new field "fieldOfView4f SFVec4f -1 -1 -1 -1"
> - change existing "fieldOfView MFFloat" default to []
> - spec says:
> Authors: please use fieldOfView4f, consider fieldOfView deprecated.
> Implementors: if fieldOfView.count <> 0 then use fieldOfView,
> else use fieldOfView4f
>
> 3. (Please let's not do this :) ) Modify X3D classic encoding grammar
> to allow [ ] around SFVec4f values.
>
> I can see that Don may be leaning towards this (since you thought
> this is already how X3D classic encoding works a few days ago) but it
> would be a very unoptimal solution IMHO:
>
> - One, because it means escalating a small change into a big
> change. Changing "OrthoViewport.fieldOfView" is about one single field
> in single node. Changing X3D classic grammar means changing the
> grammar and parsing. And the grammar should be consistent, so it would
> likely spiral into allowing [ ] for other types as well, like SFVec3f.
>
> - The 2nd reason is that it's an incomplete fix anyway. While it
> will allow new browsers (that implement new grammar) to handle both
> old and new X3D models (whether author used [ ] or not aroud
> "OrthoViewport.fieldOfView")... But
>
> A. The old browsers (implementing original grammar) will not be
> able to read files using "OrthoViewpoint { fieldOfView -1 -1 1 1 }",
> they will throw parsing
> error exceptions. I understand it's a minor issue, old browsers are
> not supposed to handle X3D 4.1, but users do not like paying attention
> to version changes. Users assume (correctly!) that versions changes
> generally don't cause problems.
>
> B. We still have compatibility break if someone used PROTO with
> IS for "OrthoViewport.fieldOfView". This PROTO field type will need to
> change.
>
> C. We still have compatibility break for other APIs using X3D
> (like CGE Pascal API, but I suspect all other API like from Java etc.
> -- unless one introduces overloads to handle both types).
>
> Thanks for the discussion. Let's keep going toward a solution that is
> the best compromise :)
>
> Regards,
> Michalis
>
>
> czw., 19 gru 2024 o 20:26 Brutzman, Donald (Don) (CIV)
>
>
> <brutzman at nps.edu> napisał(a):
> >
> > Thanks for thinking about alternatives. In general, however, we don't
> repeat functionality, in accordance with DRY principles:
> >
> > Wikipedia: Don't repeat yourself
> >
> https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDon%27t_repeat_yourself&data=05%7C02%7Cbrutzman%40nps.edu%7Ca798d8810015488b460008dd20d133db%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C638702806790110709%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=EUA%2FyLVNpeDBd9%2FvGiI%2FBdWCee3S8PjV%2FsD9vDFO2U0%3D&reserved=0
> <https://en.wikipedia.org/wiki/Don't_repeat_yourself>
> >
> > 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: GPU Group <gpugroup at gmail.com>
> > Sent: Thursday, December 19, 2024 10:55 AM
> > To: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org
> >
> > Cc: Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>; Michalis
> Kamburelis <michalis.kambi at gmail.com>; 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:
> TextureProjectorparallel.fieldOfView
> >
> > IDEA: _add_ another field with different name, with a sentinel value
> default
> > fieldOfView4f SFVec4f -1 -1 -1 -1
> > Then in run code, if that field is set at its default, use the original
> MFFloat field, else use the new SFVec4f field.
> > -Doug
> >
> >
> > On Wed, Dec 18, 2024 at 9:39 PM Michalis Kamburelis via x3d-public <
> x3d-public at web3d.org> wrote:
> >
> > Hi Don,
> >
> > AD A -
> >
> > No, when writing the SFVec4f in X3D classic encoding, the square
> > brackets "[ ... ]" cannot be used. I believe my understanding matches
> > both the spec and all existing X3D implementations.
> >
> > 1. The example you noticed (on
> >
> https://www.web3d.org/documents/specifications/19776-2/V3.3/Part02/EncodingOfFields.html#SFVec4f
> > ) ... shows MFVec4f, not SFVec4f .
> >
> > It's indeed a bit misleading, as the spec section titled "5.20
> > SFVec3f and MFVec3f" describes both MF- and SF- variants. And the
> > example "fooVec3d [ 1.000000000001 42 666.35357878 32.6, 7 94
> > 0.100000000007 143.998 ]" lacks any annotation. Adding there a
> > description would help: "This is an example of MFVec4f in classic
> > encoding, fooVec3d contains here two 4-dimensional vectors." .
> >
> > 2. On the same page, the text higher makes it clear that "square
> > brackets" are used for multiple-value fields: """Multiple-valued
> > fields are written as an ordered list of values enclosed in square
> > brackets and separated by whitespace."""
> >
> > 3. The grammar on
> >
> https://www.web3d.org/documents/specifications/19776-2/V3.3/Part02/grammar.html
> > confirms it:
> >
> > """
> > mffloatValue ::=
> > sffloatValue |
> > [ ] |
> > [ sffloatValues ] ;
> >
> > ....
> >
> > sfvec4fValue ::=float float float float ;
> > """"
> >
> > No square brackets for sfvec4fValue . (And that's good I think; square
> > brackets are consistently used in X3D classic encoding for lists of
> > values.)
> >
> > I do find the grammar very helpful to resolve such questions :) It's
> > unambiguous, and implementations (using my own) follow it literally.
> >
> > So, I think my concern still stands. Changing
> > OrthoViewport.fieldOfView type (MFFloat -> SFVec4f) would break
> > parsing of all the models in X3D classic encoding (and VRML 2.0) that
> > specify value of this field. They use right now square brackets [ .. ]
> > (necessary for MFFloat with > 1 value), which are not allowed for
> > SFVec4f.
> >
> > I honestly don't think there's a way to avoid it, except reverting
> > this spec change. I cannot change in our implementation
> > OrthoViewport.fieldOfView to SFVec4f -- I have users using classic
> > encoding, and VRML 2.0 too, we cannot really break it. And maintaining
> > exceptional treatment in the parser (to allow both MFFloat and
> > SFVec4f) is not maintainable, we cannot have special rules like this
> > (that depend on node and field name) at the parser level.
> >
> > I know that we could change the grammar (to allow [ ... ] in SFVec4f)
> > but IMHO we should not change the grammar (which will complicate
> > parsing) just to account this one single exceptional change to one
> > field in one node.
> >
> > AD B - No, I didn't describe any special handling in our parser. And
> > such exceptions during parsing would be really hard to maintain, I
> > deliberately don't want them. Parser should not have any special rules
> > for specific nodes or fields -- this makes parser code more obvious.
> >
> > On the contrary -- we parse OrthoViewport.fieldOfView as MFFloat
> > now. Only later (after parsing) we just look at the count of MFFloat.
> > When it's less than 4, we treat the remaining numbers as if they were
> > default. But this is nice "local" code near OrthoViewport.fieldOfView
> > logic. It's *not* part of the parser.
> >
> > Regards,
> > Michalis
> >
> > czw., 19 gru 2024 o 03:06 Brutzman, Donald (Don) (CIV)
> > <brutzman at nps.edu> napisał(a):
> > >
> > > Thanks for looking at this Michalis.
> > >
> > > A. Sorry but I'm not clear about what you are saying... Went to look
> at the existing ClassicVRML encoding and it is showing [square brackets]
> for SFVec4f:
> > >
> > > X3D Classic VRML encoding, clause 5 encoding of fields, 5.22 SFVec4f
> and MFVec4f
> > >
> https://www.web3d.org/documents/specifications/19776-2/V3.3/Part02/EncodingOfFields.html#SFVec4f
> > >
> > > The SFVec4f field specifies a four-dimensional (4D) single-precision
> vector. An MFVec4f field specifies zero or more 4D single-precision
> vectors. SFVec4f's and MFVec4f's are encoded as four ISO C floating point
> values (see ISO/IEC 9899) separated by whitespace.
> > > EXAMPLE
> > > fooVec3f [ 1 42 666 -43.8, 7 94 0 0.0001 ]
> > >
> > > ... And so am expecting your SFVec4f example would look the same,
> with [square brackets] around numeric values. Please advise what you
> think.
> > >
> > > OrthoViewpoint { fieldOfView [ -1 -1 1 1 ] }
> > >
> > >
> > > B. Depending on that, am next wondering... you describe how the
> current MFFloat approach already requires additional special handling by
> your parser if an incorrect number of values is encountered. If there is a
> difference regarding [square brackets] for SFVec4f then maybe a parser
> adjustment for that might be possible too... Or, even if they are the same,
> maybe just keeping your error-handling parser for v3.3 content the same
> (also for backwards reliability) is a good idea also.
> > >
> > > C. We are currently working on ClassicVRML Encoding spec for v4.0 now,
> so if any problems are found then we can resolve them.
> > >
> > > D. I found several problems with the Grammar... Dick and I also
> discussed them yesterday. When time permits, will post about that soon.
> > >
> > > Have fun with X3D ClassicVRML Encoding! 🙂
> > >
> > >
> > > 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: x3d-public <x3d-public-bounces at web3d.org> on behalf of Michalis
> Kamburelis via x3d-public <x3d-public at web3d.org>
> > > Sent: Wednesday, December 18, 2024 5:37 PM
> > > To: Extensible 3D (X3D) Graphics public discussion <
> x3d-public at web3d.org>
> > > Cc: Michalis Kamburelis <michalis.kambi at gmail.com>;
> 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:
> TextureProjectorparallel.fieldOfView
> > >
> > > The change of OrthoViewpoint.fieldOfView from MFFloat to SFVec4f
> > > breaks compatibility (badly) for X3D classic encoding, from what I can
> > > see.
> > >
> > > Previously (when OrthoViewpoint.fieldOfView is MFFloat, so in X3D <=
> > > 4.0 and VRML 2.0) this was valid:
> > >
> > > OrthoViewpoint { fieldOfView [ -1 -1 1 1 ] }
> > >
> > > And this was "undefined how it works (spec doesn't say what happens
> > > for < 4 values), but at least parsing was OK" (CGE made some effort to
> > > tolerate it):
> > >
> > > OrthoViewpoint { fieldOfView [ -1 -1 ] }
> > >
> > > Now (when OrthoViewpoint.fieldOfView is SFVec4f) both above are
> > > invalid, at parsing. One has to write this:
> > >
> > > OrthoViewpoint { fieldOfView -1 -1 1 1 }
> > >
> > > ... but the new form is invalid if loaded into a browser that expects
> > > OrthoViewpoint.fieldOfView to be old MFFloat.
> > >
> > > And, before anyone suggests this: It's not reasonable for X3D browsers
> > > to define OrthoViewpoint.fieldOfView with one type for X3D >= 4.1, and
> > > another type for older X3D versions. At least I cannot imagine
> > > maintaining this exceptional behavior throughout the codebase :) We
> > > need to have a one definition of OrthoViewpoint with one type for
> > > fieldOfView, otherwise we cause a big complication (also for
> > > developers using our API).
> > >
> > > So, I'm a bit baffled what to do. If I change
> > > OrthoViewpoint.fieldOfView to SFVec4f, I *will* break some X3D models
> > > for users and I will get bugreports about it. If I don't, I will not
> > > be compatible with X3D 4.1. For now, I choose the latter.
> > >
> > > Regards,
> > > Michalis
> > >
> > > czw., 19 gru 2024 o 01:42 John Carlson via x3d-public
> > > <x3d-public at web3d.org> napisał(a):
> > >
> > >
> > >
> > > >
> > > > I’m imagining there will be changes to C++ SAI. Once new types are
> in place I can attempt to test. I suggest getting an X3DUOM out soon, so I
> can regenerate my fieldTypes.js file, which affects all my serializers.
> > > >
> > > > No one is using my serializers that I know of, so this particular
> change won’t probably affect anyone. They would have to update, and I
> don’t currently recommend that.
> > > >
> > > > Bug reports are welcome:
> > > >
> > > >
> https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fcoderextreme%2FX3DJSONLD%2Fissues&data=05%7C02%7Cbrutzman%40nps.edu%7Ca798d8810015488b460008dd20d133db%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C638702806790133840%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=RD2m3DWAfH1d5QDVg9p4%2FNlXnkSInA%2FxG5bnd%2F1pHIM%3D&reserved=0
> <https://github.com/coderextreme/X3DJSONLD/issues>
> > > >
> > > >
> > > > AFAIK, this does not affect X3D JSON, since MFFloat and SFVec4f are
> represented by arrays.
> > > >
> > > > If you recommend tweaking X3DUOM before your release, I can see what
> I can do, but it’s not currently a priority for me. Reading the X_ITE
> component into Blender is higher priority.
> > > >
> > > > Someone speaking up can change the priority.
> > > >
> > > > John
> > > >
> > > > On Wed, Dec 18, 2024 at 6:00 PM Brutzman, Donald (Don) (CIV) via
> x3d-public <x3d-public at web3d.org> wrote:
> > > >>
> > > >> During a specification editors' meeting yesterday, Dick and I made
> another step forward.
> > > >>
> > > >> Mantis 1398: OrthoViewpoint fieldOfView type needs to be SFVec4f,
> not MFFloat
> > > >> https://mantis.web3d.org/view.php?id=1398
> > > >>
> > > >> namely
> > > >>
> > > >> If specialty methods for homogeneous transformations (or other
> operations) are needed by SAI implementations, they can receive specialized
> definitions to match.
> > > >> It is important to remember that (a) no nodes currently use
> homogenous coordinates, and (b) ClipPlane definition of a half-plane is
> different than the two parallel-projection extents.
> > > >> A graceful approach not requiring implementation changes might be
> adding prose to Clause 5 field definitions noting alternate usages may
> occur. For example, appended to the fist sentence, "or other usage of a
> 4-tuple."
> > > >>
> > > >> We applied that change in draft X3D 4.1 Architecture, also
> committed into git and pushed online.
> > > >>
> > > >> 5.3.20 SFVec4d and MFVec4d
> > > >>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD//Part01/fieldTypes.html#SFVec4dAndMFVec4d
> > > >> 5.3.21 SFVec4f and MFVec4f
> > > >>
> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD//Part01/fieldTypes.html#SFVec4fAndMFVec4f
> > > >>
> > > >> ==========================
> > > >> 5.3.20 SFVec4d and MFVec4d
> > > >> The SFVec4d field or event specifies a three-dimensional (3D)
> homogeneous vector, or other usage of a 4-tuple. An MFVec4d field or event
> specifies zero or more SFVec4d values. 3D homogeneous vectors. SFVec4d's
> and MFVec4d's are represented as a 4-tuple of double-precision floating
> point values (see 5.3.4 SFDouble and MFDouble). The allowable form for a
> double-precision floating point number is defined in the specific encoding.
> > > >> The default value of an uninitialized SFVec4d field is (0 0 0 1).
> The default value of an MFVec4d field is the empty list.
> > > >> 5.3.21 SFVec4f and MFVec4f
> > > >> The SFVec4f field or event specifies a three-dimensional (3D)
> homogeneous vector, or other usage of a 4-tuple. An MFVec4f field or event
> specifies zero or more SFVec4f values. 3D homogeneous vectors. SFVec4f's
> and MFVec4f's are represented as a 4-tuple of single-precision floating
> point values (see 5.3.5 SFFloat and MFFloat). The allowable form for a
> single-precision floating point number is defined in the specific encoding.
> > > >> The default value of an uninitialized SFVec4f field is (0 0 0 1).
> The default value of an MFVec4f field is the empty list.
> > > >> ==========================
> > > >>
> > > >> If anyone can think of any reason not to restrict validation of
> OrthoViewpoint fieldOfView to SFVec4f, instead of an MFFloat array of
> length 4, please speak up. Am hoping to apply this change next to
> validation tools next, improving quality assurance and author confidence
> that a model is valid. Avoiding run-time errors and maintaining
> consistency, with no harm to existing X3D models or implementations, is
> important.
> > > >>
> > > >> Have fun with high-quality X3D! 🙂
> > > >>
> > > >>
> > > >> 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: Brutzman, Donald (Don) (CIV) <brutzman at nps.edu>
> > > >> Sent: Friday, December 13, 2024 1:14 PM
> > > >> To: Holger Seelig <holger.seelig at yahoo.de>; X3D <
> x3d-public at web3d.org>
> > > >> Cc: 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:
> TextureProjectorparallel.fieldOfView
> > > >>
> > > >> 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://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHomogeneous_coordinates&data=05%7C02%7Cbrutzman%40nps.edu%7Ca798d8810015488b460008dd20d133db%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C638702806790151701%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=%2B0692Ipq84A8Mo8IxSIa9LaK8DV1PD%2B9nMWL%2FjvYUbg%3D&reserved=0
> <https://en.wikipedia.org/wiki/Homogeneous_coordinates>
> > > >>
> https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FHomogeneous_coordinates%23%2Fmedia%2FFile%3ARationalBezier2D.svg&data=05%7C02%7Cbrutzman%40nps.edu%7Ca798d8810015488b460008dd20d133db%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C638702806790164107%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=WDz40uRYwtPE3R%2FLIFURKLUaHvA%2BcuK%2BQIdfIwLebb0%3D&reserved=0
> <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://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fcreate3000.github.io%2Fx_ite%2F&data=05%7C02%7Cbrutzman%40nps.edu%7Ca798d8810015488b460008dd20d133db%7C6d936231a51740ea9199f7578963378e%7C0%7C0%7C638702806790176380%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C60000%7C%7C%7C&sdata=LboRmmKHHvcVGr3DesWxfIea4ahYZNkm8bj0JQ%2FTXrE%3D&reserved=0
> <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
> > > >>
> > > >>
> > > >> _______________________________________________
> > > >> x3d-public mailing list
> > > >> x3d-public at web3d.org
> > > >> http://web3d.org/mailman/listinfo/x3d-public_web3d.org
> > > >
> > > > _______________________________________________
> > > > x3d-public mailing list
> > > > x3d-public at web3d.org
> > > > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
> > >
> > > _______________________________________________
> > > x3d-public mailing list
> > > x3d-public at web3d.org
> > > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
> >
> > _______________________________________________
> > x3d-public mailing list
> > x3d-public at web3d.org
> > http://web3d.org/mailman/listinfo/x3d-public_web3d.org
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20241220/a7be79a2/attachment-0001.html>
More information about the x3d-public
mailing list