I have an object that is similar on one side and the other. However, the UV image editor UNwrapped it so that each half has slightly different vertex positions. How can I get it so that all the vertices line up?
If those UVs are exactly the same, you can align UVs to some common vertex and then rotate one UV with enabled vertex snapping and snap the rotation to some vertex of the other UV.
- Enable snapping Shift+Tab
- Set Snap UV Element to Vertex Ctrl+Shift+Tab
- Set Selection Mode to Island Ctrl+Tab
- Grab one island G and align it to corresponding vertex of the other UV island
- Change Selection Mode to Vertex, select the common vertex and hit Shift+S to set Cursor to Selected, so you can use this vertex as a pivot point in next step
- Change Pivot to 2D Cursor .
- This is quite unpredictable but hopefully it will work - rotate the UV R and hover your cursor over vertices on the second UV until the rotation snap to it.
If your UVs are not exactly the same, you can then select all vertices and press W > Remove Doubles to merge vertices close to each other.
I don't think there is a tool in blender which allows you to do it automatically (you may try to ask another question how to do it by scripting though). Here's my method which uses a pinning option. Place two UV islands close to each other. Enable the snapping tool (vertex) and snap all the external vertices of one island to the vertices of the other to match islands' shapes.
Now select the rim of the first island (Alt+RMB) and press P to pin it. Press L to select the whole island and hide it (H). Repeat the pinning process for the second island. Next unhide the first one with Alt+H, select both (A) and unwrap again. Finally unpin everything with Alt+P.