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?
-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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