[x3d-public] X3D 4.0 specification problem: OrthoViewpoint.fieldOfView
John Carlson
yottzumm at gmail.com
Fri Dec 20 09:37:50 PST 2024
It might be good to add the 4 method parameter anyway, even if no
specification changes are made. Ideally, Java would have a way to limit
array length parameters in a declaration, but I’m not seeing that
happening. What a fine way to fix array bounds errors, probably at the
expense of performance.
Ada anyone? Maybe Pascal, Rust or TypeScript can have fixed sized array
parameters?
John
On Fri, Dec 20, 2024 at 11:21 AM John Carlson <yottzumm at gmail.com> wrote:
> I know I don’t have a vote, but my serializers and I’m pretty sure
> X3dToJava.xslt are broken currently, as of my tests yesterday. Details
> below.
>
> On Fri, Dec 20, 2024 at 10:03 AM Brutzman, Donald (Don) (CIV) via
> x3d-public <x3d-public at web3d.org> wrote:
>
>> [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
>>
>>
> I think you meant SFVec4. My tendency, after reading Michalis’ message
> and my tests is to retain MFFloat.
>
>>
>> -
>> - 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
>>
>>
> I think brackets for MF fields is appropriate. Removing brackets is a
> breaking change. I don’t think that SF fields should have brackets.
>
> I understand that XML does not have this issue. This will break my
> serializers to remove brackets. Changes to X3DJSAIL might fix the
> problem, but I haven’t seen that yet. Please test X3dToJava.xslt with the
> new field type in place. Try Holger’s Library examples with
> OrthoViewpoint.fieldOfView. The issue is 4 parameters (SFVec4f) versus 1
> parameter (MFFloat). Yes, we could add another method to
> OrthoViewpoint.java to handle the first case.
>
> I believe Holger’s examples are VolumeEmitter.x3d and
> Connectors.x3d/Connections.x3d.
>
> If you have an XML file to test, please share so that everyone can test.
>
> This doesn’t affect X3D JSON because brackets or arrays are used in both
> cases.
>
> Seasons Greetings!
>
>>
>> -
>>
>> 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
>> _______________________________________________
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>>
>
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