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?
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.
There, we can simply sample the user-defined function as needed and produce
matrices that are guaranteed to be affine.
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?
-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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