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[Numbers] Inheritance and ValJO ? (Was: Where to define "quaternion"?)


After the discussion quote below, the conclusion was to go with

However, it would make "Quaternion" fail the "ValJO" definition[1]
that mandates that all constructors be private.

Would a protected constructor really be an issue?
[In the case of "Quaternion", the subclass constructor would only
perform additional validation (cf. below for details).]


[1] https://blog.joda.org/2014/03/valjos-value-java-objects.html

On Mon, 03 Dec 2018 10:31:42 +0100, Gilles wrote:

On Mon, 3 Dec 2018 03:56:02 +0000, Matt Juntunen wrote:
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

Someone else?

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

It seems indeed the perfect case for inheritance.

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.

What do you see as a potential issue?

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

Perhaps. I've certainly only used them to represent 3D rotations. Are
there any other use cases from commons-numbers?

Not within [Numbers], but that's the point of those very low-level
components/modules: they are common utilities used by higher-level

Given that "QuaternionRotation" is a special case of "Quaternion",
it is logical to keep the latter at a lower-level, namely in
[Numebers], and make [Geometry] depend on it.

  * 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.

Is "slerp" applicable to a general "Quaternion", or does it assume
the additional requirements of "QuaternionRotation"?
[Same question applies to all utilities in order to decide where to
define them.]

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


Could you please update it so that it inherits from "Quaternion"?


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
least have a reference implementation and baseline functionality for
commons-geometry that we can modify later based on what's decided

My questions below are a start; I'm waiting for answers.
Code duplication is bad (TM).


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:

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
slerp as well as several other geometry-oriented methods, such as
conversion to/from axis-angle representations and creation from
rotations. It's not quite ready for a merge yet since I still need
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
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
 * 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.


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,




Apache Commons Geometry. Contribute to darkma773r/commons-geometry
development by creating an account on GitHub.

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
committers." page.


> I think two convenience divide methods performing qr^{-1} and
> for q
> and r would be useful, but I couldn't think of nice names for

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
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
end up
creating inverse instances and throwing them away a lot and I
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
domain (see also "Commons Geometry", another new component not yet
released) but I may be wrong...



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