With three.js, I use a quaternion to rotate an arrow (located on the unit sphere). I have a complete script in this link: https://jsfiddle.net/PhilipZhu/937wov02/1/ Most of the codes are for setups. The relavant parts are typed below: // define a quaternion let u = -0.3; // scaling factor of non…

I followed the math process inside Three.js with a simple test. Assume we have point (1,0,0) and quaternion (x,y,z,w). Quaternioning the point as if it is THREE.Vector3 uses directly applyQuaternion and the transformed vector is: (ww+xx-zz-yy, 2xy+2zw, 2xz-2yw ). When the point is quaternioned as i…

As far as I know, only quaternions in a form { w: cos(θ), x: exsin(θ), y: eysin(θ), z: ezsin(θ) }, where e is the quaternion direction unit vector, are used to represent rotation in 3D space. By that definition, they are unit quaternions. So if you non-uniformly scale quaternion components, you ne…

Maybe this will help you? [image] Quaternion - Axis, Angle Visualization Resources I’ve been using quaternions. Because rotation in space is not easy, I was looking for a simple visualization. I found a lot of theory about quaternions and a workable converter. http://ww…

Yes, I know. But I’m more interested in the implementation of the function than how to use, and what might be the advantage of implementing Object3’s quaternion rotation in a special way. For example, it might be interesting to know if it is related to numerical stability when you have to transform …

[image] PhilipZhu: I’m more interested in the implementation of the function From Object3D.js : applyQuaternion( q ) { this.quaternion.premultiply( q ); return this; } From Quaternion.js : premultiply( q ) { return this.multiplyQuaternions( q, this ); } multiplyQuaternions( a, b ) { // …

See also [image] Quaternion - method .setFromBasis( e1, e2, e3 ) Resources These posts and examples are about movement on a curve. Struggling with paths - #14 by hofk Car Racing - For lovers of fast cars! MotionAlongCurve MovementOnCurve CarRacing However, the solut…

What you showed is the only correct definintion of quaternion multiplication, and both Vector3 and Object3 use the correct implementation for quaternion multiplication defined in Quaternion.js. I don’t think it explains my question. Please see the demo: [image] PhilipZhu: three.js non-unit quat…

[image] PhilipZhu: What you showed is the only correct definintion of quaternion multiplication … <snip> … I don’t think it explains my question. My message was about “I’m more interested in the implementation of the function”.

[image] PavelBoytchev: My message was about “I’m more interested in the implementation of the function”. Right. It’s also helpful to have what you posted here for sure.

I’m not good with quaternions. I played a bit with your code. If the arrow originates from (0,0,0), it is easier to show larger arrows … and the green/blue arrows are different again, but it is easier to see the differences. Here are a few observations that may give a clue (although it might be just…

This is very interesting! Thanks for sharing this. Then I’m assuming that the reason for threejs to have this discrepency is not due to some numerical stability that I would have imagined. Just that it’s convenient to manage rotation by matrix.

How does three.js handle rotations by non-unit quaternions?

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hofk June 1, 2023, 7:50pm 6

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How does three.js handle rotations by non-unit quaternions?

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