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Re: [Numbers][Geometry] Where to define "quaternion" (Was: Making Quaternion a VALJO)

```On Sat, 01 Dec 2018 12:56:34 +0100, Gilles wrote:
```
```Hello.

On Sat, 1 Dec 2018 06:05:31 +0000, Matt Juntunen wrote:
```
```Hi guys,

FYI, I've been working on a quaternion-related class named
```
QuaternionRotation for commons-geometry (see link below). It includes
```slerp as well as several other geometry-oriented methods, such as
```
conversion to/from axis-angle representations and creation from basis rotations. It's not quite ready for a merge yet since I still need to
```finish the Euler angle conversions.

I did not use the Quaternion class from commons-numbers since I
```
wanted to focus solely on using quaternions to represent 3D rotations.
```I felt like the commons-numbers class was too general for this.
```
```
We need to explore further how to avoid duplication.

Some questions:
* Should "QuaternionRotation" inherit from "Quaternion"?
* Should "Quaternion" be defined in [Geometry] (and removed from
[Numbers])?
* Are some utilities defined in "QuaternionRotation" general
such that they could be part of the [Numbers] "Quaternion" API.
An example might be the transformation between quaternion and
matrix (represented as a double[3][3])?

The second consideration could apply to any computation that does
not require types defined in [Geometry].  For example, interpolation
is a purely quaternion-internal operation.
```
```
s/second/third/

```
```
It looks to me that it should be possible to come up with a design
that defines "rotation" in [Geometry] which uses a "quaternion"
defined in [Numbers].
Otherwise, one would wonder why "Complex" is also not in [Geometry]
(for 2D rotations).

Best regards,
Gilles

```
```
Regards,
Matt

https://github.com/darkma773r/commons-geometry/blob/transforms/commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/threed/QuaternionRotation.java

[https://avatars1.githubusercontent.com/u/3809623?s=400&v=4]<https://github.com/darkma773r/commons-geometry/blob/transforms/commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/threed/QuaternionRotation.java>

darkma773r/commons-geometry<https://github.com/darkma773r/commons-geometry/blob/transforms/commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/threed/QuaternionRotation.java>
Apache Commons Geometry. Contribute to darkma773r/commons-geometry
development by creating an account on GitHub.
github.com

________________________________
From: Gilles <gilles@xxxxxxxxxxxxxxxxxxxxx>
Sent: Friday, November 30, 2018 9:37 AM
To: dev@xxxxxxxxxxxxxxxxxx
Subject: Re: [numbers] Making Quaternion a VALJO

On Fri, 30 Nov 2018 14:22:45 +0000, Steve Bosman wrote:
```
```> and I have also emailed an ICLA.
```
```
```
```Not received/acknowledged yet.
```
```
I am now listed on the "Persons with signed CLAs but who are not
(yet)
committers." page.
```
```
Welcome!

```
```> I think two convenience divide methods performing qr^{-1} and
r^{-1}q
> for q
> and r would be useful, but I couldn't think of nice names for
them.
```
```
```
```What are the use-cases?
Why aren't "multiply" and "inverse" enough?
```
```
I must admit I'm new to quaternions and stumbled into the project
while
trying to improve my understanding so I'm not going to claim great
knowledge of how common these operations are. I was primarily
thinking of
Quaternion Interpolation - SLERP and SQUAD. It seems to me that you
end up
```
creating inverse instances and throwing them away a lot and I thought
```it
would be good to reduce that overhead.
```
```
Surely, the class "Quaternion" is minimal but, before adding to
the API, we be careful to have use-cases for low-level operations.
Those mentioned above seems more high-level, tied to a specific
released) but I may be wrong...

Regards,
Gilles

```
```
Steve
```
```
```
```
```
```

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