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

```I was just thinking from a practical standpoint. My current QuaternionRotation class is still in my working branch for GEOMETRY-14 and so isn't really accessible to anyone. If I can finish it up in its current state (hopefully very soon) and get it merged, then someone else will be able to work with it and blend the functionality with commons-numbers.

Here are some notes on your questions from before:

* Should "QuaternionRotation" inherit from "Quaternion"?

That would work conceptually. The quaternions in the QuaternionRotation class are standard quaternions that meet two other criteria: 1) they are unit length, and 2) their scalar component is greater than or equal to zero (in order to standardize the angles involved). The one sticking point here is that I'm not sure how this fits with the VALJO concept. If we can get this sorted, then this very well may be the best option.

* Should "Quaternion" be defined in [Geometry] (and removed from [Numbers])?

Perhaps. I've certainly only used them to represent 3D rotations. Are there any other use cases from commons-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 conversion to rotation matrix and slerp are the best candidates here. The other methods rely on core classes from commons-geometry, namely Vector3D.

One more note: I decided to make a separate package for 3D rotations in my working branch for GEOMETRY-14, so QuaternionRotation is now at https://github.com/darkma773r/commons-geometry/blob/transforms/commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/threed/rotation/QuaternionRotation.java.

-Matt
________________________________
From: Gilles <gilles@xxxxxxxxxxxxxxxxxxxxx>
Sent: Sunday, December 2, 2018 3:57 PM
To: dev@xxxxxxxxxxxxxxxxxx
Subject: Re: [Numbers][Geometry] Where to define "quaternion" (Was: Making Quaternion a VALJO)

On Sun, 2 Dec 2018 19:20:03 +0000, Matt Juntunen wrote:
> Unless anyone objects, I'm going to continue with what I'm working on

I certainly don't object on your working to improve the geometry
code, but wherever that work overlaps with code being worked on
elsewhere (in this case, the "Quaternion" class), then we'd
rather have a discussion happening here first.

> with QuaternionRotation and create a merge request. That way, we'll
> at
> least have a reference implementation and baseline functionality for
> commons-geometry that we can modify later based on what's decided
> here.

My questions below are a start; I'm waiting for answers.

Regards,
Gilles

>
> -Matt
> ________________________________
> From: Gilles <gilles@xxxxxxxxxxxxxxxxxxxxx>
> Sent: Saturday, December 1, 2018 9:40 PM
> To: dev@xxxxxxxxxxxxxxxxxx
> Subject: 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.
>>>>
>>>>
>>>> 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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