Real quick one here tonight on a persistent UV Unwrap mistake I still see people asking about.
Sometimes in Blender when you’re ready to do a UV Unwrap on an object, the preview in the UV/Image Editor doesn’t look right.
What I mean is you might start with the default cube, then scale it into a very flat rectangle as in my screen shots. Then you tab into edit mode and Mark Seams by pressing Control-E.
Now, I usually would split my window here by right-clicking on the top divider bar and set my right hand window to UV/Image Editor. Then when you go to unwrap in the main window (pressing the U key), you would expect to see a flattened rectangle in the right-hand UV window.
But no, you get a bunch of squares instead.
If you export this template and lay graphics on it, forcing them into the squares, then it will usually expand correctly. I’ve done it when I just couldn’t figure out what had went wrong and I was tired of wrangling with it.
The best course of action is to actually fix the problem, though. The answer is in my 3rd paragraph.
If you scale, translate and rotate in OBJECT mode, those changes aren’t relayed to the UV Unwrapper. They don’t make it through to the EDIT mode.
To circumvent this you can either:
1. Make all scaling changes in EDIT mode.
2. If you’ve made changes in OBJECT mode, you can apply those changes by going to ‘Object>Clear/Apply/Apply Scale/Rotation to ObData’. Once you select this all the changes you did will be applied to the mesh, where the UV Unwrapper can get at them.
Now, if you tab back into Edit mode, then Unwrap again, you’ll see the preview in your UV/Image Editor now reflects the current shape of your mesh.
Incidentally, this happens in Blender 2.49b and earlier, AND in the latest 2.5 Alpha (2.52.0 as of this writing). It’s not really a bug, but just something you need to be aware of.
Hopefully this helps anyone who might get stuck like I was. Let me know if you have any questions.