# Talk:Point reflection

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Field: Geometry

## Reflection?

I signal an incoherence in terminology: the reflection article says a reflection has only one eigenvalue -1 (and all its examples adhere to this) so a "point reflection" is not a reflection (actually, in the plane I would consider it a rotation rather than a reflection). I think the proper term is "point symmetry" (which I just redirected here; it used to point to symmetry group for no apparent reason), and would suggest a corresponding page move. But I'm not particularly acquainted with English geometry literature, so I'll stand corrected if this is common terminology. However the reflection through the origin article does call the use of "reflection" an abuse of language. Marc van Leeuwen (talk) 15:40, 4 April 2010 (UTC)

Point reflections do not fall under the framework for a reflection described in the reflection (mathematics) article, but it is nonetheless the common terminology for this transformation (see Google books for examples). "Point symmetry" refers to a slightly different concept, in the same way that reflection symmetry is different from reflection. Jim (talk) 16:02, 4 April 2010 (UTC)

## Merge

I’ve just merged inversion in a point and reflection through the origin (the latter of which I wrote, not knowing of this page) to this page, as they cover the same topic.

The only meaningful distinctions I can see that could be made would be:

• affine vs. vector (reflection through any point vs. reflection through the origin);
• low dimensions (2D, 3D) for novices vs. arbitrary dimension (n-dimensions) for initiates.

For such a simple topic I think these topics can all effectively be covered in a single page, though the current page could use some work.

—Nils von Barth (nbarth) (talk) 09:28, 14 April 2010 (UTC)