[x3d-public] SFRotation default value spec. inconsistency

Sun Feb 16 09:00:02 PST 2025

> Should both (all, everywhere) list the same default value ? 

Yes, would be my vote.
 Thanks, 
Joe

-----Original Message-----
From: Holger Seelig <holger.seelig at yahoo.de>
Sent: Feb 16, 2025 12:33 AM
To: Andreas Plesch <andreasplesch at gmail.com>
Cc: Joseph D Williams <joedwil at earthlink.net>, X3D <x3d-public at web3d.org>
Subject: Re: [x3d-public] SFRotation default value spec. inconsistency

I think the default value is 0 0 1 0 for rotations. It’s already the case for the old JavaScript VRML 2.0 spec: 
https://www.web3d.org/documents/specifications/14772/V2.0/part1/fieldsRef.html#SFRotation 
As well as the Field Type Reference say 0 0 1 0:

https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/fieldTypes.html#SFRotationAndMFRotation

On the other hand all rotation values in the spec have a 0 0 1 0 rotation as well:

https://www.web3d.org/specifications/X3Dv4Draft/ISO-IEC19775-1v4.1-CD/Part01/Architecture.html

Holger

--
Holger Seelig
Leipzig, Germany

holger.seelig at yahoo.de
https://create3000.github.io/x_ite/

Am 16.02.2025 um 06:11 schrieb Andreas Plesch <andreasplesch at gmail.com>:
I agree, probably the best default value for a unit quaternion is 0 0 0 1.

However, X3D does not concern itself with quaternions, only axis-angle rotations.

So the original question remains: Part 1 has axis-angle 0 0 1 0 as default while the JS SAI spec. has 0 1 0 0. Should both list the same default value ?

If yes, which one ? I would vote for 0 1 0 0 since rotations around Y seem more common.

-Andreas

On Sat, Feb 15, 2025 at 11:04 PM <joedwil at earthlink.net (mailto:joedwil at earthlink.net)> wrote:
Doesn't this mean that the _best_ default value, for no rotation, is 'legally' for unit quaternion = 0 0 0 1 
because the square root of the sum of the squares of all four components does = 1 ?
0 0 0 0 would not be a legal unit quaternion.
While the axis-angle default is 0 0 1 0 as appears in Part 1 is mostly for convenience
since many value combinations can produce zero rotation? 
Also sure shows why axis-angle is so much easier to work with when typing numbers,
pitch and yaw and roll for all. 
Thanks,
Joe

-----Original Message-----
From: Andreas Plesch <andreasplesch at gmail.com (mailto:andreasplesch at gmail.com)>
Sent: Feb 14, 2025 11:36 AM
To: Holger Seelig <holger.seelig at yahoo.de (mailto:holger.seelig at yahoo.de)>
Cc: X3D <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>, Joseph D Williams <joedwil at earthlink.net (mailto:joedwil at earthlink.net)>
Subject: Re: [x3d-public] SFRotation default value spec. inconsistency

Let me just add for clarity that the length (or norm) of a quaternion includes the fourth, the scalar component. The norm is the square root of the sum of the squares of all four components.

Only unit quaternions represent rotations. A (0,0,0,0) quaternion does not represent any rotation (but of course exists outside of rotations).

Andreas

PS: To add back in some fuzziness, a unit quaternion can only represent a rotation up to 360 degrees. I think there is a mechanism to use non-unit quaternions for larger rotations.

On Fri, Feb 14, 2025 at 10:22 AM Holger Seelig <holger.seelig at yahoo.de (mailto:holger.seelig at yahoo.de)> wrote:
All quaternions must be normalized to be a legal rotation, so the length of the quaternion must always be one. 
Holger--
Holger Seelig
Leipzig, Germany

holger.seelig at yahoo.de (mailto:holger.seelig at yahoo.de)
https://create3000.github.io/x_ite/

Am 14.02.2025 um 15:38 schrieb Joe D Williams via x3d-public <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>:

> So, sensibly, a zero rotation around any axis corresponds to the "zero unit Quaternion" (0, 0, 0, 1 XYZW),  

Right. Not sure but  0 0 0 0 for unit quaternion might not be legal. I think the values must compute to1 to be legal?
Thanks,
Joe

-----Original Message-----
From: Andreas Plesch <andreasplesch at gmail.com (mailto:andreasplesch at gmail.com)>
Sent: Feb 10, 2025 12:37 PM
To: Joe D Williams <joedwil at earthlink.net (mailto:joedwil at earthlink.net)>
Cc: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>
Subject: Re: [x3d-public] SFRotation default value spec. inconsistency

https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#_node_rotation
has indeed (0, 0, 0, 1 XYZW) as a default value.

This is difficult to interpret as a rotation around an axis since the corresponding axis would be at first glance (0 0 0).

x3dom converts quaternion (0, 0, 0, 1 XYZW) to (axis),angle (0,0,0),0 as does https://www.andre-gaschler.com/rotationconverter/ .

On the other hand both SFRotation (0 0 1 0) and SFRotation (0 1 0 0) are also represented by quaternion (0, 0, 0, 1 XYZW).

So, sensibly, a zero rotation around any axis corresponds to the "zero unit Quaternion" (0, 0, 0, 1 XYZW), making it a useful default value for quaternions. But that does not help with choosing a default axis for the SFRotation value.

This will rarely matter. A use case may be when a SFRotation is initialized to the X3D default in a Proto but then only the angle is modified by a Proto script with the assumption that the axis is (0 0 1).

-Andreas

On Mon, Feb 10, 2025 at 12:57 PM Joe D Williams <joedwil at earthlink.net (mailto:joedwil at earthlink.net)> wrote:
not zerp,  zero

-----Original Message-----
From: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>
Sent: Feb 10, 2025 9:50 AM
To: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>, X3D Graphics public mailing list <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>
Cc: Joe D Williams <joedwil at earthlink.net (mailto:joedwil at earthlink.net)>, Andreas Plesch <andreasplesch at gmail.com (mailto:andreasplesch at gmail.com)>
Subject: Re: [x3d-public] SFRotation default value spec. inconsistency

I think the 0 0 1 0 should be used everywhere for default axis-angle. 
I thinkI see 'zerp' unit quaternions (as in gltf as 0 0 0 1  XYZW) 
Thanks,
Joe

-----Original Message-----
From: Extensible 3D (X3D) Graphics public discussion <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>
Sent: Feb 10, 2025 8:44 AM
To: X3D Graphics public mailing list <x3d-public at web3d.org (mailto:x3d-public at web3d.org)>
Cc: Andreas Plesch <andreasplesch at gmail.com (mailto:andreasplesch at gmail.com)>
Subject: Re: [x3d-public] SFRotation default value spec. inconsistency

The JS SAI spec. at https://www.web3d.org/documents/specifications/19777-1/V3.3/Part1/functions.html#FieldServices

does not list functions for SFColorRGBA, only SFColor. There may be an earlier report. -Andreas

On Mon, Feb 10, 2025 at 11:31 AM Andreas Plesch <andreasplesch at gmail.com (mailto:andreasplesch at gmail.com)> wrote:
https://www.web3d.org/documents/specifications/19775-1/V4.0/Part01/fieldTypes.html#SFRotationAndMFRotation

specifies that (0 0 1 0) is the value of an uninitialized SFRotation given as (x y z a).

However, the JS SAI spec. in table 7.18 in https://www.web3d.org/documents/specifications/19777-1/V3.3/Part1/functions.html#SFRotationInstanceCreationFunction

effectively makes (0 1 0 0) the default value if no parameters are provided.

The inconsistency does not have much of an impact since both are 0 rotations but I believe (0 1 0 0) - a 0 rotation around y - may have been intended as the default.

-Andreas

-- 
Andreas Plesch
Waltham, MA 02453

-- 
Andreas Plesch
Waltham, MA 02453

-- 
Andreas Plesch
Waltham, MA 02453

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-- 
Andreas Plesch
Waltham, MA 02453

-- 
Andreas Plesch
Waltham, MA 02453

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