Matrix4 extractBasis question

Questions
1

Hello!

const xAxis = new THREE.Vector3();
const yAxis = new THREE.Vector3();
const zAxis = new THREE.Vector3();
object.matrixWorld.extractBasis(xAxis, yAxis, zAxis);

const xAxis = new THREE.Vector3(1, 0, 0);
const yAxis = new THREE.Vector3(0, 1, 0);
const zAxis = new THREE.Vector3(0, 0, 1);
const quat = new THREE.Quaternion().setFromRotationMatrix(object.matrixWorld);
xAxis.applyQuaternion(quat);
yAxis.applyQuaternion(quat);
zAxis.applyQuaternion(quat);

According to my understanding, the axis calculated by the two methods should be the same, but I got different results.

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2

In some cases, they are the same, but sometimes they are not.
I am very confused about this, what can cause different situations to happen?

3

One possible reason is when the object is scaled.

4

just a guess,
had some complex positioning to achieve as well, and the only safe method for me was to
matrix.decompose the object, then use the outputs (so the quaternion in you case).

5

How different?

I would expect some minor numerical differences, but not much…

6

@rookie, have you checked that these differences aren’t an abstraction of 0 under eulers constant…?

If a number is followed by e-N this is typically a sign that the number is a numerical representation of a number divided by a power which results in numbers minutely close to 0 but not absolutely 0, this can look confusing in the console because some of those numbers can start with positive numbers, eg… 5.294685e-56

EDIT: a good way to check this is if a value contains “e-” you should be able to practically assume that it’s 0, or a representation thereof…

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