OK, I've contacted the author of UU3D about my problem and this is his response, in case it's of use to anyone else:
Hi,
There's two main menu options in Unwrap3D, 2D Tools and 3D Tools. 2D Tools will only modify UV coordinates, they don't touch geometry. While all commands under 3D Tools modify geometry, they don't touch UV coordinates.
On the subject of welding UV coordinates, actually, no UV coordinates can be welded or unwelded in Unwrap3D (internally speaking). As you probably noticed, you can select a single UV face and drag it anywhere, so it is never connected in any sense.
Internally in Unwrap3D, all faces have their own UV coordinates, so this is why the program behaves the way it does. It was initially designed like this, because it simplified UV mapping for many things.
When you do a 'Weld UVs' in Unwrap3D, this command will only move UV coordinates to nearby UV coordinates that are within tolerance range. Nothing is physically welded.
When you do a 'Pack UVs' separated by connectivity in Unwrap3D, this command needs to build an edge structure from the UV coordinates as they are shown on screen. So if you have overlapping UV coordinates, this may confuse the edge building process.
This command only works well when you have UV coordinates that are not overlapping.
As for the welding/unwelded of geometry, this should work as expected.
Vertices are internally welded. You can easily see the effect of welding vertices by switching to a Smooth-shaded rendering mode. After vertices are welded, the hard edges are replaced with smooth edges. And if you try to select a face in 3D and move it, you will know it is connected by the fact that it doesn't break off from the rest of the geometry.
But, back to your problem. What I would suggest in your case if you want to move one set of UV coordinates to another, and align it exactly, is to use the numerical Move UVs option, e.g. Edit | Move | Arbitrary. First, move one set 'absolutely' to UV coordinate 0,0. Then move the other set 'absolutely' to UV coordinate 0,0.
Now, both sets should be aligned exactly on top of each other. You can now select both sets and drag them anywhere you want.
I hope some of that was helpful.
Regards,
Brad Bolthouse
Hi,
There's two main menu options in Unwrap3D, 2D Tools and 3D Tools. 2D Tools will only modify UV coordinates, they don't touch geometry. While all commands under 3D Tools modify geometry, they don't touch UV coordinates.
On the subject of welding UV coordinates, actually, no UV coordinates can be welded or unwelded in Unwrap3D (internally speaking). As you probably noticed, you can select a single UV face and drag it anywhere, so it is never connected in any sense.
Internally in Unwrap3D, all faces have their own UV coordinates, so this is why the program behaves the way it does. It was initially designed like this, because it simplified UV mapping for many things.
When you do a 'Weld UVs' in Unwrap3D, this command will only move UV coordinates to nearby UV coordinates that are within tolerance range. Nothing is physically welded.
When you do a 'Pack UVs' separated by connectivity in Unwrap3D, this command needs to build an edge structure from the UV coordinates as they are shown on screen. So if you have overlapping UV coordinates, this may confuse the edge building process.
This command only works well when you have UV coordinates that are not overlapping.
As for the welding/unwelded of geometry, this should work as expected.
Vertices are internally welded. You can easily see the effect of welding vertices by switching to a Smooth-shaded rendering mode. After vertices are welded, the hard edges are replaced with smooth edges. And if you try to select a face in 3D and move it, you will know it is connected by the fact that it doesn't break off from the rest of the geometry.
But, back to your problem. What I would suggest in your case if you want to move one set of UV coordinates to another, and align it exactly, is to use the numerical Move UVs option, e.g. Edit | Move | Arbitrary. First, move one set 'absolutely' to UV coordinate 0,0. Then move the other set 'absolutely' to UV coordinate 0,0.
Now, both sets should be aligned exactly on top of each other. You can now select both sets and drag them anywhere you want.
I hope some of that was helpful.
Regards,
Brad Bolthouse