The context of this question: I am writing technical documentation in the field of computational science, i.e. simulating physical systems on the computer.

I am writing about a method, which takes in an existing mesh, creates the mirror image and joins the results. This way, if we have a symmetric problem, we need to create only half the geometry with our meshing tool, and we can then apply the mirroring operation.

What I want to know is the correct preposition for the following sentence:

"Mirror the geometry by(?) the user-provided plane"

  • Is the idea that a user provides a plane and the method mirrors its geometry?
    – Juhasz
    Sep 3, 2019 at 15:29
  • 2
    Your question is actually nothing to do with the word mirror (which could just as well have been write about, explain, or whatever). It's just that you're talking about the geometry of [something] (or possibly talking about doing something [by] using something else, I dunno). Answer the question by / using / with / through examples - there's no fixed "correct" preposition. Sep 3, 2019 at 15:30
  • @Juhasz correct. Thus, the method mirrors the geometry with the plane. What I want to express is that the plane is the mirror. If I would do the reverse, i.e. the cut a geometry using the plane, I would write "cut the geometry with the plane"
    – Dohn Joe
    Sep 3, 2019 at 15:36
  • The verb "mirror" doesn't require a preposition before the direct object as it is transitive (e.g., "The user-provided plane mirrored the existing mesh into an image...). If you're changing into the passive voice such that the subject performing the mirroring becomes an indirect object, then the preposition "by" is always used for that no matter what the verb is (e.g., "The existing mesh was mirrored into an image by the user-provided plane."). Sep 3, 2019 at 15:37
  • @BenjaminHarman The user-defined plane is passive in this sentence because it's an imaginary reference surface. I don't think it's supposed to be performing an action, so no action can be done by it.
    – mRotten
    Sep 3, 2019 at 16:51

1 Answer 1


Let me know if I understand the operation: You have a function that reflects some mesh model ("geometry" in your sentence). To do this, you need the user to provide a plane for the reflection operation (the "user-provided plane"). Every point on the model is then duplicated on the other side of the plane at a location defined by 1) the inverse of the normal component of the original point and 2) the parallel component of the original point (both relative to the user-defined plane).

In this context, you're asking for a preposition to use to describe how the original mesh model is mirrored with respect to the plane.

If I have that right, use one of:

Mirror the geometry about the user-provided plane

Mirror the geometry across the user-provided plane

You might also consider using reflect instead of mirror, since the former more often has an object of a preposition. I'm not sure if using reflect would make this sentence more clear to your reader, but that replacement makes it more clear that about and across are better choices as the preposition for "user-provided plane".

  • 1
    +1 for reflect
    – Jim
    Sep 4, 2019 at 3:56

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