Trying to figure out how the mirror works

here is what i’m trying to figure out

this is what you get when you move an object then apply the mirror modifier (of course setting up the origin at the cursor/center)

this is what you get when you move the object, apply the modifier then rotate it

and this is when you move, rotate, then apply the modifier

i’m using the snap by face trick to rotate some objects to faces. but to do this you need to play with the cursor, and gizmo. thus when you reapply the mirror to your rotated object you get something like #3. and you guessed it, what i need is #2. so if someone could help me understand this that would be nice

By default the mirror modifier will mirror across the origin of the object in local space. Local means the axis of the object, while global means the axis of the world.

When you’re in edit mode, moving stuff like vertices or edges or polygons around will not move your origin. So if your origin is centered to the world and you rotate the vertices of the cube in edit mode. What you’ll get is number 2 where the mirror stays the same, but your model changes. What you’re doing in number 3 is rotating the object, which means it also rotates the origin.

If you want to see the axis of the object you can go to object properties under the “Viewport display” tab and click the axis option.

Top middle of the screen, you can set your transforms to be in local or global space.

Bonus round : If you want it to mirror in global space. There’s an option to use an object as the focus of the mirror modifier. So you can add an empty to the scene, align it with the world, and select that as your mirror object

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the trick i found to snap meshes by faces moves the object. so i guess i’m good to find a new way of doing. the trick can be seen here. this is not a big deal as i can snap the mesh manually by rotating it. but if i could snap to the face it would have been much better