Quaternion.identity, what does "identity" mean?

I know what Quaternion.identity does, but I don’t understand what “identity” means in this context.
I’ve been wondering about this for several years now.

It’s named after the identity matrix.

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Aaaaah perfect!
Thank you :slight_smile:

This too but it’s all basically the same idea. You multiply something by identity and it comes out as it started.

https://en.wikipedia.org/wiki/Identity_element

“No transformation” Queternion. Same logic as identity matrix. In case of Quaternion it is 0, 0, 0, 1

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? I would expect
1 0 0 0
0 1 0 0
0 0 1 0
0 0 0 1

…for an identity matrix. Why is it only one row?

Because it is a quaternion, not a matrix, and quaternion only has 4 components in it. (X, Y, Z, W in games, although in math papers it can be abcd, ijkr, and so on).

Identity transform - for a quaternion - is X=0, Y=0, Z=0, W=1.

When storing rotations, XYZ components store rotation axis scaled by factor of Sin(rotAngle/2), and W stores Cos(rotAngle/2). Because 0 degree angle has Cos==1, and Sin==0, we get 0, 0, 0, 1

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