Separating and Connecting UVs
Blender offers an unusual way to separate and connect parts of the UVs, but once you get used to it, it’s quite useful.
Separating UVs
The quickest method for separating UVs is to use the Select Split tool. Select the faces you want to separate, press Y, and they’ll be separated so you can now move them independently of one another. You can also access this option from the Select menu on the header.
You’ve already learned that on the UVs, Blender only shows the faces you’ve selected in the 3D View. But here’s an interesting fact to keep in mind: When you select only a face (or a group of faces) in the 3D View and move it on the UVs, it moves independently and becomes separated from the rest of the UVs. You can only manipulate the visible UVs, and when you do so, they are separated from the UVs that are currently hidden.
Another way of separating UVs is just to unwrap the faces you want to separate again. Select them from the 3D Model, unwrap them, and they’ll be separated.
One other method for separating UVs is to use the Hide and Unhide features of Blender (H and Alt + H), which are also available in the UV/Image Editor. Select the faces you want to separate, press Ctrl + I to invert the selection, and then move the remaining faces. Press Alt + H to reveal all the UVs and you’ll see that those faces have been separated.
Connecting UVs
Sometimes, a complex mesh can be more easily unwrapped by its parts and then joined as needed to create the least distortion possible.
Blender has a rule: only vertices that are welded in the 3D mesh can be welded on the UVs. This means that you can snap or even weld (with the welding tool from the W menu) two vertices and they’ll be in exactly the same place, but they won’t actually be merged together. Thus, when you move them, you’ll actually move only one of them.
That said, to merge vertices on the UVs that are also welded in the 3D model, you just have to put them in the same place by welding them or snapping them to another vertex.
One way to find out exactly which vertices are adjacent to each other is to use the Sync selection mode between the UVs and the 3D mesh; with this method, if you select a vertex in the mesh or on the UVs, it will show the shared vertices that should go with it in other UV islands as well. Another option is to temporarily activate the Shared Vertex selection to see which vertices are in the same place in the 3D model.
Stitch is a tool that can be very helpful when connecting UVs. You can find it on the UVs menu in the header and its shortcut is V. Select some vertices in a border of a UV island and press V; a preview will show you where those vertices should go in order to be joined to other vertices on the UVs. If you like what you see, left click to apply and if you don’t, right click to cancel the stitching.