[x3d-public] computed orientation_changed output

[Brutzman, Donald (Don) (CIV)]

Draft Specification pros is welcome. This isn't always easy, but it is an excellent path towards clarity. In this case we might need to adapt a figure as well. Thanks for considering the possibilities!

v/r Don
________________________________
From: x3d-public <x3d-public-bounces at web3d.org> on behalf of Andreas Plesch via x3d-public <x3d-public at web3d.org>
Sent: Saturday, August 31, 2024 8:48:14 AM
To: Holger Seelig <holger.seelig at yahoo.de>
Cc: Andreas Plesch <andreasplesch at gmail.com>; X3D <x3d-public at web3d.org>
Subject: Re: [x3d-public] computed orientation_changed output

I think the issue is that the spec. only defines the toVector (as the tangent) but is silent on the fromVector. It is a reasonable assumption that the fromVector is implied as 0,0,-1 ("forward") and most implementations will do that. But in theory it could be any vector.

An additional ambiguity is that there are two possible rotations from a vector to another vector. One is using the inverted axis of the other. But as long as these rotations are only used to actually be applied as rotations, this may not matter as both lead the same result.

Andreas

On Sat, Aug 31, 2024, 6:14 AM Holger Seelig <holger.seelig at yahoo.de<mailto:holger.seelig at yahoo.de>> wrote:
It is possible to calculate a rotation from fromVector to toVector, but these rotations have an arbitrary upVector.

And yes, it would be better to have a defined upVector to make these rotations stable.

Holger

--
Holger Seelig
Leipzig, Germany

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

Am 30.08.2024 um 23:45 schrieb Patrick Dähne <pdaehne at gmail.com<mailto:pdaehne at gmail.com>>:

Unfortunately, it is not possible to implement NurbsOrientationInterpolator because it is not specified how to calculate the „up“ vector (the tangent of the curve only specifies the z axis, but neither the x nor y axis of the local coordinate system). The same applies to any other hypothetical „xOrientationInterpolator“.

Bye,

Patrick


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