Question about global and local axis

[Kp4ws]

I’m having a hard time wrapping my head around the global and local axis. On a high level, I understand what they mean. The part I’m confused about is when I rotating/scaling/moving the object.

I have two questions

1. The local axis will only have different vectors if the object has been rotated right?
2. (main question): If an object has different local vectors, do I typically want to use those when scaling, or rotating ?

It seems like such a simple concept but it keeps tripping me up haha.

[FedPete]

1. yes.
2. A blender object has a lot of properties, main material, modifiers, location x,y,z, rotation x,y,z,width, height, volume, mass …
   But also a thing called the mesh. The mesh you can edit. if you edit the mesh, for example, rotate. the local stays the same. Even scale the mesh the object scaling stays 1.

But scaling the object does not change the mesh (yeah it scales, but the data is the same. Most blender functions work on these properties, incl. the mesh. So it’s best to have the object scale to one. If you apply object scale it will (internally) set the mesh to the object properties.

This works the same for rotation, if you apply rotation, then the inner mesh has been updated with rotation data. Its difficult then to restore the original rotation.

[NP5]

2. It depends! There are occasions when it is very useful to have local vectors that still match the object’s changed rotation. The problem comes in that modifiers and some other tools use the base data that was the object state before it was rotated or scaled.

So there is no one answer that covers all situations.

Perhaps do not apply until you need too, more or less covers it? But that can lead to later problems and wondering why. Practice and experience in the end.

[Kp4ws]

Oh I didn’t even realize there was a difference between the objects and the meshes, I was just assuming they were all the same thing. Thanks for bringing this up!

So when you go into edit mode, that’s the mesh you’re editing, whereas object mode is the object?
Also when you’re using rotate or scale, are these usually performed in object mode then?

[Kp4ws]

I see I see, thanks very much! Yeah I think I just need more practice and experience until I get fully used to the different scenarios

[FedPete]

Yes.
In edit mode the local axis stays the same.

If you rotate the cube object. The local axis changes.
Then you go into edit mode, select all the 8 vertices, rotate. The local axis will be the same as before.
If you reset, rotation by hand on the object (0,0,0), then the mesh is still rotated. And it will be difficult to make it the original cube.

And the best way is to use rotate on the object.
Scale on the other hand, is best done in edit mode.
It can also be done in Object mode (scaling), but most people forget, to apply scale in object mode (so that the mesh inside follows the new dimension), When forgotten some strange things can happen in armature, arrays etc.