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--></style></head><body lang=EN-US link=blue vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><ul style='margin-top:0in' type=disc><li class=MsoListParagraph style='margin-left:0in;mso-list:l0 level1 lfo1'>three-dimensional (3D) homogeneous vector </li></ul><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>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</p><p class=MsoNormal>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. </p><p class=MsoNormal>Thanks,</p><p class=MsoNormal>Joe</p><p class=MsoNormal><o:p> </o:p></p><div style='mso-element:para-border-div;border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='border:none;padding:0in'><b>From: </b><a href="mailto:michalis.kambi@gmail.com">Michalis Kamburelis</a><br><b>Sent: </b>Sunday, March 13, 2022 3:08 PM<br><b>To: </b><a href="mailto:yottzumm@gmail.com">John Carlson</a><br><b>Cc: </b><a href="mailto:x3d-public@web3d.org">X3D Public Mailing List (x3d-public@web3d.org)</a><br><b>Subject: </b>Re: [x3d-public] Mantis 1392: 5.3.20 SFVec4d and MFVec4d defaultvalue (0 0 0 1) or (0 0 0 0) ?</p></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The description of 4D vectors states their purpose: "a</p><p class=MsoNormal>three-dimensional (3D) homogeneous vector".</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The 4D value "0 0 0 1" means "3D position at (0,0,0), when interpreted</p><p class=MsoNormal>as (3D) homogeneous vector".</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The 4D value "0 0 0 0" would mean "invalid value, when interpreted as</p><p class=MsoNormal>(3D) homogeneous vector".</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Let's keep the "0 0 0 1" as default. I don't see any reason to change,</p><p class=MsoNormal>"0 0 0 1" makes sense. (One could also argue that "0 0 0 0" makes</p><p class=MsoNormal>sense, but it is a flip a coin, they both can be argued as "better</p><p class=MsoNormal>defaults". So, no reason to break compatibility.)</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Regards,</p><p class=MsoNormal>Michalis</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>niedz., 13 mar 2022 o 19:48 John Carlson <yottzumm@gmail.com> napisał(a):</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> My guess is it has to do with a perspective transformation.</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> John</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> On Sun, Mar 13, 2022 at 1:35 PM Brutzman, Donald (Don) (CIV) <brutzman@nps.edu> wrote:</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Clause 5.3.20 SFVec4d and MFVec4d lists default value as (0 0 0 1)</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Why not (0 0 0 0) similar to other SFVec/MFVec fields?</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/Part01/fieldTypes.html#SFVec4dAndMFVec4d</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Similarly for 5.3.21 SFVec4f and MFVec4f</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4-CD1/Part01/fieldTypes.html#SFVec4fAndMFVec4f</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Entered as</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Mantis 1392: 5.3.20 SFVec4d and MFVec4d default value (0 0 0 1) or (0 0 0 0) ?</p><p class=MsoNormal>>> https://www.web3d.org/member-only/mantis/view.php?id=1392</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> all the best, Don</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> --</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Don Brutzman Naval Postgraduate School, Code USW/Br brutzman@nps.edu</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> Watkins 270, MOVES Institute, Monterey CA 93943-5000 USA +1.831.656.2149</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> X3D graphics, virtual worlds, Navy robotics https:// faculty.nps.edu/brutzman</p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>><o:p> </o:p></p><p class=MsoNormal>>> _______________________________________________</p><p class=MsoNormal>>> x3d-public mailing list</p><p class=MsoNormal>>> x3d-public@web3d.org</p><p class=MsoNormal>>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org</p><p class=MsoNormal>><o:p> </o:p></p><p class=MsoNormal>> _______________________________________________</p><p class=MsoNormal>> x3d-public mailing list</p><p class=MsoNormal>> x3d-public@web3d.org</p><p class=MsoNormal>> http://web3d.org/mailman/listinfo/x3d-public_web3d.org</p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>_______________________________________________</p><p class=MsoNormal>x3d-public mailing list</p><p class=MsoNormal>x3d-public@web3d.org</p><p class=MsoNormal>http://web3d.org/mailman/listinfo/x3d-public_web3d.org</p><p class=MsoNormal><o:p> </o:p></p></div></body></html>