I'm very noob to uv editing, but i found very strange the lack of symmetry tools in the uv editor. Any idea?

p.s.
I can't mirror the half of the obj, i need both the side of the uv to be different part of the texture...

Unfortunately there's no such built in option.

But, you could try this script (I've just updated it today ):
http://myara.web.fc2.com/mMirrorUV.html

I've included it in my mSymm2 plugin too, but this one is still in beta.
http://www.si-community.com/community/viewtopic.php?f=4&p=18655#p18655

Is there something you can't do? Thx you!

i'm sorry, i can't really make it work, it gives me this error:

# ERROR : You need to select a polygon subcomponent. Or UV Island with Auto Sync Subcomponent and Polygon Filter Selection activated

Can you explain me how to make it work?

In the website you can find the instructions.

It's a little tricky. It works with polygon component selections, not UVs.

Open your Texture Editor Preferences. Set your Sync Method Settings in Components.
Set Selection filter in Polygons in your Selection Menu (up and right). Just like when you want to select a polygon component.
Select an UV Island. It will automatically select the polygon components.
Run the Script

Does this script, mirror the uvs? i seems to me that, it mirrors uvs ( isn't that function the same ad "flip uvs"?

I would like one ot this two thing:

1 - edit from both side of a symmetrical uv. The purpose is to edit one time the uv, for both sides

or
2 - once i've done the first half, copy/mirror a side of an uv to the other

Is this possibile?

The only way i found is to cut the mesh, symmetrize it, mirror the corrispondig half...

1. Not possible

2. If I understood you, this script should do the trick.

Have you watched the animated gif in the download website?

Select a UV Island with Sync Method in Components and selection filter in Polygon.
You'll have UV islands selected in your Texture Editor and SI will automatically select the polygon components in the viewer.

Now, in the script GUI, select which part do you want to mirror.
Ex: -X
It will mirror the UVs from the selected polygons that are in -X

Then click where do you want to flip the UV.

watch from 4:25
[vim]39883619/[/vim]

Of course you could do it in SI without this script.

You would have to select half of your polygon, then flip the UV with Mirror Horizontal / Vertical, change the pivot and move the UV island to fit the other half.

Ok i got it, it works, but... it wasn't what i wanted to do. This script it's like to scale the uv -100% in X, right? It's the same thing?

Once i've made the uv for the right side of a mesh, i would like to copy that uv, mirror and past on the other side of the mesh.

Let's see if I understand you.
You want to edit the UV from the +X side while keeping the -X UV somewhere else. And then copy the +X side UV to the -X side?

I don't think it is possible. And to be honest, I don't see the point.
I would just create one side of the object, create UVs, mirror polygon, and mirror the UV.

Don't confuse UV coordinates with XYZ because the conversation gets messy.

This script asumes you have an UV island overlapped. Meaning you have the same UV for both sides of the polygon. So It takes only a half side of your selection, detect the extremes position in your UV island, and flip it with the pivot in your island extreme, so you'll have now a mirrored UV with both sides like the GIF is showing.

The common Mirror Horizontal function you have in your Texture Editor flip all selected UV with the pivot in their center.

Thx you, now i understand what you mean.
iI tought that cutting the obj, mirror it, filp di uv was a bad trick. i'm very new to uv mapping...