[x3d-public] X3D, Blender, and which way is up.

[Brutzman, Donald (Don) (CIV)]

Your definition sounds good to me.  Glad to hear that this is consistently sorted out and implemented in recent Blender version.

Here are X3D Tooltip hints for Viewpoint and orientation:

  *
X3D Tooltips: Viewpoint
  *
Viewpoint provides a specific location and direction where the user may view the scene. Viewpoints are the primary way for a user to navigate within a scene, and for an author to show critical aspects of a model. Unless modified by the orientation field, the default direction for a Viewpoint to look is along the -Z axis.
  *
https://www.web3d.org/x3d/content/X3dTooltips.html#Viewpoint

  *
X3D Tooltips: Viewpoint orientation
  *
https://www.web3d.org/x3d/content/X3dTooltips.html#Viewpoint.orientation
  *
[orientation accessType inputOutput<https://www.web3d.org/x3d/content/X3dTooltips.html#accessType>, type SFRotation<https://www.web3d.org/x3d/content/X3dTooltips.html#SFRotation> CDATA<https://www.web3d.org/x3d/content/X3dTooltips.html#CDATA> "0 0 1 0"]
Rotation (axis, angle in radians) of Viewpoint, relative to default -Z axis direction in local coordinate system.
Hint: this is orientation _change_ from default direction (0 0 -1).
Hint: complex rotations can be accomplished axis-by-axis using parent Transforms.
Warning: for VR/AR/MR/XR users wearing a head-mounted display (HMD), animating this field may induce motion sickness.

Improvements always welcome.  Have fun with 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: x3d-public <x3d-public-bounces at web3d.org> on behalf of vmarchetti--- via x3d-public <x3d-public at web3d.org>
Sent: Sunday, November 24, 2024 11:39 AM
To: X3D-Public <x3d-public at web3d.org>
Cc: vmarchetti at kshell.com <vmarchetti at kshell.com>
Subject: [x3d-public] X3D, Blender, and which way is up.

I've seen that the email thread starting with the minutes of the last Blender-X3D support call had a subthread about the orientation conventions that glTF, Blender, and X3D use.

I recommend Michalis' answer at https://web3d.org/pipermail/x3d-public_web3d.org/2024-November/020882.html.

One confusing aspect is that not only do Blender and glTF disagree about which axis is forward, they disagree about what the word "forward" means.

For Blender, the word "forward" refers to the axis that the viewer is looking along when they are viewing the front of the model.
The viewer is translated from the model in the -Y direction, and they are looking in the +Y direction. That, +Y,  is Blender "forward"

glTF defined "forward" by the model.Looking at the first sentence of the of section 3.4 of the glTF specification. https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html#coordinate-system-and-units,

glTF uses a right-handed coordinate system. glTF defines +Y as up, +Z as forward, and -X as right; the front of a glTF asset faces +Z.


glTF says the "forward" refers to the direction the asset, a.k.a. model is facing and the spec shows this example picture . In Blender terminology this model is oriented "-Z forward"



[boombox.png]

The X3D standard has the same orientation convention as glTF, by virtue of the X3D default placement of the Viewpoint at a Z=+10 position and looking in the -Z direction. That is why in Blender terminology the X3D convention should be considered -Z forward. The code in the Blender extensions server was changed to this default for X3D import and export on Nov 4 2024 and this default is in release 2.4.0 of this Blender extension.

Vince Marchetti



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