Quaternion to/from slice?

nalgebra
1

It seems there is no Quaternion<f64>::from_slice() or quat.as_slice() - or am I missing something?

2

Hi!

You’re right, there are no such methods. Though they could be added. Would you like to open an issue for this? Perhaps even a pull request them if you which?

Regarding quat.as_slice(), one thing you can already do is quat.coords.as_slice().

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3

OK cool, tracking issue here: https://github.com/rustsim/nalgebra/issues/697 :slight_smile:

4

btw I realized I accidentally didn’t set the category here… maybe move to nalgebra ?

5

seems there is no as_mut_slice() on quat.coords ?

Or in more detail, DerefMut isn’t implemented for Quaternion<f64>

6

There is already a quat.coords.as_mut_slice(), and DerefMut is alrealy implemented for Quaternion<f64>: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=595a042e802f5e2178922a7b3e6bad2c

Perhaps your quat is not mutable?

7

Sorry, my mistake, I had a UnitQuaternion<f64>: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=a0ea53b8b03fca56281e0c228d9af9a1

Am I supposed to first convert that back to a Quaternion<f64> ?

8

ah okay - the trick is as_mut_unchecked()

example: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=ed3bd1d817174dfd888d393165afffe1

:slight_smile:

9

You should be careful with .as_mut_unchecked() though. It is not unsafe, but you may end up with surprising results if you modify the slice in such a way that the resulting UnitQuaternion is no longer of unit size: its norm should always be equal to 1 so it can actually represent a rotation.

This is actually the main difference between UnitQuaternion and Quaternion: if you need a rotation, use UnitQuaternion which only supports operations that preserve its unit length (except for those _unchecked methods). If you need a general quaternion which does not necessarily have a unit size, use Quaternion.

1 Like