Gilles,
> I had a (quick) look; is it necessary to split functionality among "Transform"
> (in "core") and its subinterfaces/classes in other modules? IOW, if
> "Transform"
> can only be affine, it looks strange to have "AffineTransform" (re)defined.
This is a documentation issue. The name "affine transform" only applies to
affine spaces such as Euclidean space. Spherical space is not an affine space.
The "Transform" interface is intended to represent transforms with the desired
properties regardless of whether the space is affine or not. This was not clear
in the docs since the word "affine" is listed as an implementation requirement
on the "Transform" interface. I've updated the docs and userguide to clarify
this.
> I'm also a bit puzzled by the "AbstractAffineTransformMatrix" that seems to
> only contain convenience methods for internal use (whereas having them
> "protected" put them in the public API).
That class also contains other matrix-specific methods (eg, "determinant") and
the overridden "preservesOrientation". Good point on the protected methods,
though. I've moved them into the internal "Matrices" utility class.
-Matt
________________________________
From: Gilles Sadowski <gillese...@gmail.com>
Sent: Sunday, January 19, 2020 9:06 AM
To: Commons Developers List <dev@commons.apache.org>
Subject: Re: [geometry] Rename Transform to AffineTransform
Hi.
Le sam. 18 janv. 2020 à 23:14, Matt Juntunen
<matt.juntu...@hotmail.com> a écrit :
>
> Gilles,
>
> >> There, we can simply sample the user-defined function
> > I'm not sure I understand.
>
> Just an implementation detail. We need to pass some sample points through the
> user-defined function in order to construct an equivalent matrix.
>
> > Throwing an exception if the transform does not abide by
> > the requirements?
>
> Yes.
>
> I just submitted a PR on Github with these changes. I also realized that the
> EuclideanTransform class as discussed exactly matches the definition of an
> affine transform so I renamed it to AffineTransform. No other names were
> changed.
I had a (quick) look; is it necessary to split functionality among "Transform"
(in "core") and its subinterfaces/classes in other modules? IOW, if "Transform"
can only be affine, it looks strange to have "AffineTransform" (re)defined.
I'm also a bit puzzled by the "AbstractAffineTransformMatrix" that seems to
only contain convenience methods for internal use (whereas having them
"protected" put them in the public API).
Regards,
Gilles
>
> -Matt
> ________________________________
> From: Gilles Sadowski <gillese...@gmail.com>
> Sent: Saturday, January 18, 2020 1:40 PM
> To: Commons Developers List <dev@commons.apache.org>
> Subject: Re: [geometry] Rename Transform to AffineTransform
>
> Hello.
>
> 2020-01-18 15:40 UTC+01:00, Matt Juntunen <matt.juntu...@hotmail.com>:
> > Gilles,
> >
> >> If the "Transform" is intimately related to the "core" and there is a
> >> single
> >> set of properties that make it "affine" (and work correctly), I'd tend to
> >> keep the name "Transform".
> >
> > So, if I'm understanding you correctly, you're saying that since the
> > partitioning code in the library only works with these types of
> > parallelism-preserving transforms, it can be safely assumed that
> > o.a.c.geometry.core.Transform represents such a transform. Is this correct?
>
> Indeed.
>
> > One thing that's causing some issues with the implementation here is that
> > the Euclidean TransformXD interfaces have static "from(UnaryOperator<X>)"
> > methods that allow users to wrap their own, arbitrary vector operations as
> > Transform instances. We don't (and really can't) do any validation on these
> > user-defined functions to ensure that they meet the library requirements. It
> > is therefore easy for users to pass in invalid operators. To avoid this, I'm
> > thinking of removing the TransformXD interfaces completely and moving the
> > "from(UnaryOperator<X>)" methods into the AffineTransformMatrixXD classes.
>
> +1
> It is generally good to prevent the creation of invalid objects.
>
> > There, we can simply sample the user-defined function
>
> I'm not sure I understand.
>
> > as needed and produce
> > matrices that are guaranteed to be affine.
>
> Throwing an exception if the transform does not abide by
> the requirements?
>
> > Following the above, the class hierarchy would then be as below, which is
> > basically what it was before I added the TransformXD interfaces.
> >
> > commons-geometry-core
> > Transform
> >
> > commons-geometry-euclidean
> > EuclideanTransform extends Transform
> > AffineTransformMatrixXD implements EuclideanTransform
> > Rotation3D extends EuclideanTransform
> > QuaternionRotation implements Rotation3D
> >
> > commons-geometry-spherical
> > Transform1S implements Transform
> > Transform2S implements Transform
> >
> > WDYT?
>
> +1
>
> Best,
> Gilles
>
> >
> > -Matt
> >
> >
> > ________________________________
> > From: Gilles Sadowski <gillese...@gmail.com>
> > Sent: Monday, January 13, 2020 8:03 PM
> > To: Commons Developers List <dev@commons.apache.org>
> > Subject: Re: [geometry] Rename Transform to AffineTransform
> >
> > Hi.
> >
> > Le lun. 13 janv. 2020 à 04:39, Matt Juntunen
> > <matt.juntu...@hotmail.com> a écrit :
> >>
> >> Gilles,
> >>
> >> > How about keeping "Transform" for the interface name and define a method
> >> > ... boolean isAffine();
> >>
> >> I would prefer to have separate types for each kind of transform.
> >> This would make the API clear and would avoid numerous checks in the code
> >> in order to see if a particular transform instance is supported. The
> >> transform types also generally have an "is-a" relationship with each
> >> other, which seems like a perfect fit for inheritance. [1]
> >>
> >> > I don't get that it is an "accuracy" issue. If some requirement is not
> >> > met,
> >> results will be plain wrong
> >>
> >> Yes, you are correct. I was not very clear in what I wrote. The results
> >> will be completely unusable if the transform does not meet the
> >> requirements.
> >>
> >> > I wonder why the documented requirement that an "inverse transform
> >> must exist" does not translate into a method ... getInverse();
> >>
> >> Good point. All current implementations are able to provide an inverse so
> >> that method should be present on the interface.
> >>
> >> In regard to renaming the Transform interface, I had another idea. The
> >> main purpose of that interface is to provide a way for the partitioning
> >> code in the core module to implement generic transforms of BSP trees (see
> >> AbstractBSPTree.transform()). This is what leads to the requirement that
> >> the transform preserve parallelism, since otherwise, the represented
> >> region may be warped in such a way as to make the tree invalid. However,
> >> as far as I can tell, there is not a general mathematical term for this
> >> type of transform that applies to Euclidean and non-Euclidean geometries.
> >> So, my thought is to move the Transform interface to the "partitioning"
> >> package to indicate its relationship to those classes and simply name it
> >> something descriptive like "ParallelismPreservingTransform" ("parallelism"
> >> since that is the more generic, non-Euclidean form of the concept of
> >> "parallel"). The Euclidean module could then provide a true
> >> "AffineTransform" interface that extends "ParallelismPreservingTransform".
> >> The spherical module transforms would directly inherit from
> >> "ParallelismPreservingTransform" and thus avoid any incorrect usage of the
> >> term "affine". The class hierarchy would then look like this:
> >>
> >> commons-geometry-core
> >> ParallelismPreservingTransform
> >>
> >> commons-geometry-euclidean
> >> AffineTransform extends ParallelismPreservingTransform
> >> AffineTransformXD extends AffineTransform
> >> AffineTransformMatrixXD implements AffineTransformXD
> >> Rotation3D extends AffineTransform3D
> >> QuaternionRotation implements Rotation3D
> >>
> >> commons-geometry-spherical
> >> Transform1S implements ParallelismPreservingTransform<Point1S>
> >> Transform2S implements ParallelismPreservingTransform<Point2S>
> >>
> >> I think the type names here are much more descriptive and mathematically
> >> accurate. WDYT?
> >
> > I'm not convinced that such a hierarchy would enhance clarity.
> > If the "Transform" is intimately related to the "core" and there is a
> > single
> > set of properties that make it "affine" (and work correctly), I'd tend to
> > keep the name "Transform". [As long as unit tests ensure that concrete
> > implementations possess the expected properties, we are safe.]
> >
> > Regards,
> > Gilles
> >
> >> -Matt
> >>
> >>
> >> [1] https://en.wikipedia.org/wiki/Geometric_transformation
> >>
> >> ________________________________
> >> From: Gilles Sadowski <gillese...@gmail.com>
> >> Sent: Wednesday, January 8, 2020 8:16 AM
> >> To: Commons Developers List <dev@commons.apache.org>
> >> Subject: Re: [geometry] Rename Transform to AffineTransform
> >>
> >> Hi.
> >>
> >> Le mer. 8 janv. 2020 à 04:39, Matt Juntunen
> >> <matt.juntu...@hotmail.com> a écrit :
> >> >
> >> > Gilles,
> >> >
> >> > > I thought that the question was how to replace "transform"...
> >> >
> >> > I should probably clarify. I want to change the name of the Transform
> >> > class to make it clear that it only represents transforms that preserve
> >> > parallelism (eg, affine transforms). The most obvious name would be
> >> > AffineTransform
> >>
> >> How about keeping "Transform" for the interface name and define a method
> >> ---CUT---
> >> /**
> >> * Move here the doc explaining under what conditions this method can
> >> return "true".
> >> */
> >> boolean isAffine();
> >> ---CUT---
> >> ?
> >>
> >> Gilles
> >>
> >> > like I suggested but I want to make sure that no one objects to this for
> >> > design or mathematical reasons.
> >> >
> >> > > Anyways, what would be the issue(s) of a non-affine transform?
> >> > > IOW why should implementations of "Transfrom" be restricted to affine
> >> > > transform?
> >> >
> >> > Instances of Transform are used to transform hyperplanes and
> >> > hyperplane-bounded regions. If the transform is not affine, then the
> >> > computed results will not be accurate.
> >>
> >> I don't get that it is an "accuracy" issue. If some requirement is not
> >> met,
> >> results will be plain wrong; so it depends on usage: when the transform
> >> must be affine, the code being passed that instance should be able to
> >> check whether it can use it for the intended purpose.
> >>
> >> I wonder why the documented requirement that an "inverse transform
> >> must exist" does not translate into a method
> >> ---CUT---
> >> Transform<P> getInverse();
> >> ---CUT---
> >>
> >> Regards,
> >> Gilles
> >>
> >> > -Matt
> >> > ________________________________
> >> > From: Gilles Sadowski <gillese...@gmail.com>
> >> > Sent: Tuesday, January 7, 2020 6:41 PM
> >> > To: Commons Developers List <dev@commons.apache.org>
> >> > Subject: Re: [geometry] Rename Transform to AffineTransform
> >> >
> >> > Le mar. 7 janv. 2020 à 17:55, Matt Juntunen
> >> > <matt.juntu...@hotmail.com> a écrit :
> >> > >
> >> > > Gilles,
> >> > >
> >> > > > "AffineMap" (?)
> >> > >
> >> > > I think any name that doesn't include the word "transform" somehow
> >> > > would probably be confusing.
> >> >
> >> > This is supposed to be a synonym.[1]
> >> > I thought that the question was how to replace "transform"...
> >> >
> >> > >
> >> > > > Was the same "Transform" interface used in both the "euclidean" and
> >> > > > the
> >> > > "spherical" packages of "Commons Math"?
> >> > >
> >> > > Indirectly. SphericalPolygonsSet extended AbstractRegion, which
> >> > > included an applyTransform(Transform) method.
> >> >
> >> > So the "affine" requirement (in the doc) applied there too.
> >> >
> >> > Anyways, what would be the issue(s) of a non-affine transform?
> >> > IOW why should implementations of "Transfrom" be restricted to affine
> >> > transform?
> >> >
> >> > Regards,
> >> > Gilles
> >> >
> >> > [1] https://en.wikipedia.org/wiki/Affine_transformation
> >> >
> >> > > -Matt
> >> > > ________________________________
> >> > > From: Gilles Sadowski <gillese...@gmail.com>
> >> > > Sent: Tuesday, January 7, 2020 10:29 AM
> >> > > To: Commons Developers List <dev@commons.apache.org>
> >> > > Subject: Re: [geometry] Rename Transform to AffineTransform
> >> > >
> >> > > Hello.
> >> > >
> >> > > Le mar. 7 janv. 2020 à 16:00, Matt Juntunen
> >> > > <matt.juntu...@hotmail.com> a écrit :
> >> > > >
> >> > > > Hi all,
> >> > > >
> >> > > > The documentation for the o.a.c.geometry.core.Transform interface
> >> > > > (which comes from the original commons-math version) states that
> >> > > > implementations must be affine. Therefore, I think we should rename
> >> > > > this interface to AffineTransform to avoid confusion with other
> >> > > > types of transforms, such as projective transforms. Potential
> >> > > > problems with this are
> >> > > > - the fact that the JDK already has a class with the same name
> >> > > > (java.awt.geom.AffineTransform), and
> >> > >
> >> > > "AffineMap" (?)
> >> > >
> >> > > > - I'm not sure if the term "affine" can technically be applied to
> >> > > > non-Euclidean geometries, such as spherical geometry (there may be
> >> > > > nuances there that I'm not aware of).
> >> > >
> >> > > Was the same "Transform" interface used in both the "euclidean" and
> >> > > the
> >> > > "spherical" packages of "Commons Math"?
> >> > >
> >> > > Regards,
> >> > > Gilles
> >> > >
> >> > > > Anyone have any insight or opinions on this? I've created
> >> > > > GEOMETRY-80 to track this issue.
> >> > > >
> >> > > > Regards,
> >> > > > Matt
>
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