How can I position some elements precisely?

Question

How can I place these arches I made around a center (for example, the origin), in order to make all of them perfectly aligned to X,Y,Z?

Thank you in advance to the kind users

Answer 1

There are probably hundreds of ways to align objects in Blender. One easy way to align objects that have their origin points in the centers(if you have objects rotated 180° facing each other) would be to scale them to 0 using Affect Only Locations while constrained to desired axis. If you set origin to bounds center before this, it ensures the origins are at centers(this will align origins so it matters where they are). Transform pivot point must not be set to Individual Origins for this to work. It can be any other transform pivot point mode that happens to be convenient for you.

Of course since all transform operators(like G,R,S) take precise numerical inputs or you can use Mirror or Array modifiers it might make sense to place the objects precisely in the first place in this case.

Answer 2

You can use an Empty for that. Create one with Add > Empty > Plain Axes (or another one there) and make it the parent of your arch arrays. Their transforms will be local to the empty now, so you can enter precise convenient offset values (in my example its (3,0,0), (-3,0,0), (0,3,0), (0,-3,0). You can now transform the empty freely and the arches will keep their relative positions.

If you know all your arches will have the same layout you can also use a combination of an Empty and the Mirror modifier. Create an Empty again, but this time you need only one arch array and do not need to parent it. Align it with the Empty to your wished offset, add an Mirror modifier with X and Y activated and set the Empty as the mirror object. Now rotate the Empty 45° around the z-axis. This version keeps you from the hassle to maintain four array copies but obviously it will constrain you to offset them individually.