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Excellent question, thanks for asking Holger.</div>
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This issue has been carefully tracked and regularly revisited since July 2022.</div>
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<div class="elementToProof">Mantis 1398: OrthoViewpoint fieldOfView type needs to be SFVec4f, not MFFloat</div>
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<div class="elementToProof"><a href="https://mantis.web3d.org/view.php?id=1398" id="OWA4125ee98-01b1-b880-262e-29a0b5e47af6" class="OWAAutoLink">https://mantis.web3d.org/view.php?id=1398</a></div>
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<div class="elementToProof">Mantis 1468: must SFVec4f/SFVec4d fields be homogeneous?</div>
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<div class="elementToProof"><a href="https://mantis.web3d.org/view.php?id=1468" id="LPlnk373872" class="OWAAutoLink">https://mantis.web3d.org/view.php?id=1468</a></div>
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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.</div>
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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.</div>
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Reviewing the Mantis issues, additional concerns included:</div>
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<div class="elementToProof"><i>Incompatibility with prior X3D implementations.</i> 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.</div>
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<div class="elementToProof"><i>SFVec4f fields are actually not homogenous coordinates.</i> The spec uses the word "homogenous" when referring to </div>
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<div class="elementToProof"> X3D4 Architecture, Clause 5 Field type reference, 5.3.20 SFVec4d and MFVec4d</div>
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<div class="elementToProof">https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/fieldTypes.html#SFVec4dAndMFVec4d</div>
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<div class="elementToProof">"The SFVec4f field or event specifies a three-dimensional (3D) homogeneous vector." (and similarly for SFVec4d, SFVec4f and MFVec4f).</div>
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<div class="elementToProof">However none of these fields are mathematically homogeneous, see</div>
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<div class="elementToProof" style="color: rgb(51, 122, 183);">https://en.wikipedia.org/wiki/Homogeneous_coordinates</div>
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<div class="elementToProof">https://en.wikipedia.org/wiki/Homogeneous_coordinates#/media/File:RationalBezier2D.svg</div>
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<div class="elementToProof">Of related note is that ClipPlane 4-tuple "plane" field is also SFVec4f.</div>
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<div class="elementToProof">https://www.web3d.org/specifications/X3Dv4/ISO-IEC19775-1v4-IS/Part01/components/rendering.html#ClipPlane</div>
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All review welcome, hopefully I have correctly synopsized all concerns.</div>
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I think it would be beneficial to resolve this issue by reaching consensus and applying remedies as follow.</div>
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<div class="elementToProof">Omitting the over-strict word "homogenous" from the four SF/MF Vec 4f/4d definitions in future X3D 4.1 prose,</div>
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<div class="elementToProof">Updating future X3D 4.1 prose to use SFVec4f for TextureProjectorParallel fieldOfView,</div>
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<div class="elementToProof">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.</div>
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Is consensus now possible? Thanks for all careful consideration.</div>
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<p style="margin: 0in; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: "Courier New"; font-size: 9pt;">all the best, Don</span></p>
<p style="margin: 0in; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: "Courier New"; font-size: 9pt;">--</span></p>
<p style="margin: 0in; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: "Courier New"; font-size: 9pt;">Don Brutzman Naval Postgraduate School, Code USW/Br brutzman@nps.edu</span></p>
<p style="margin: 0in; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: "Courier New"; font-size: 9pt;">Watkins 270, MOVES Institute, Monterey CA 93943-5000 USA +1.831.656.2149</span></p>
<p style="margin: 0in; font-family: Calibri, sans-serif; font-size: 11pt;"><span style="font-family: "Courier New"; font-size: 9pt;">X3D graphics, virtual worlds, navy robotics https://faculty.nps.edu/brutzman</span></p>
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<div dir="ltr" id="divRplyFwdMsg"><span style="font-family: Calibri, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);"><b>From:</b> Holger Seelig <holger.seelig@yahoo.de><br>
<b>Sent:</b> Friday, December 13, 2024 11:29 AM<br>
<b>To:</b> X3D <x3d-public@web3d.org><br>
<b>Cc:</b> Brutzman, Donald (Don) (CIV) <brutzman@nps.edu>; khyoo@chungbuk.ac.kr <khyoo@chungbuk.ac.kr>; Myeong Won Lee <myeongwonlee@gmail.com><br>
<b>Subject:</b> Re: [x3d-public] X3D 4.0 specification problem: upVector field for TextureProjector, TextureProjectorParallel</span>
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<div>I just realised that TextureProjectorparallel.fieldOfView is of type SFVec4f, but OrthoViewpoint.fieldOfView is of type MFFloat.</div>
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<div>Which of the two is better?</div>
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<div>OrthoViewpoint is definitely older.</div>
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<div>I think of SFVec4f as a mathematical 4d vector.</div>
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<div><a href="https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/textureProjection.html#TextureProjectorParallel" id="OWA9984fa96-62f2-0f59-3cb5-e7dec3365b0c" class="OWAAutoLink" data-auth="NotApplicable">https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/textureProjection.html#TextureProjectorParallel</a></div>
<div style="color: rgb(0, 0, 0);"><a href="https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/navigation.html#OrthoViewpoint" id="OWA2be7b993-9d40-2b36-f72b-34a8719dd765" class="OWAAutoLink" data-auth="NotApplicable">https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/components/navigation.html#OrthoViewpoint</a></div>
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<div>Best regards,</div>
<div>Holger</div>
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--</div>
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Holger Seelig</div>
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Leipzig, Germany</div>
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holger.seelig@yahoo.de</div>
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https://create3000.github.io/x_ite/</div>
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<div>Am 08.12.2024 um 05:21 schrieb Brutzman, Donald (Don) (CIV) via x3d-public <x3d-public@web3d.org>:</div>
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However</div>
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