[x3d-public] SFRotation default value spec. inconsistency

[joedwil at earthlink.net]

> 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>
Sent: Feb 10, 2025 12:37 PM
To: Joe D Williams <joedwil at earthlink.net>
Cc: Extensible 3D (X3D) Graphics public discussion <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




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://web3d.org/pipermail/x3d-public_web3d.org/attachments/20250214/31dcfc2b/attachment.html>