Morphography tutorials
Distorting a model to improve the UV mapping
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• Introduction

I believe this tutorial has been superseded by the newer How to UV map clothing - the techniques described in there make a better job of flattening a map, with less work. However I'm keeping this active in case it should still prove useful to anyone.

Here's a technique I discovered recently - it uses certain features of UVMapper Pro, so you'll need that if you're going to follow it. The model shown in these examples is the Sandy Blouse.
Here's the problem. Say you have a re-entrant mesh like this sleeve, where the puffy bit goes in on itself. A more alert modeller would have mapped this first, before deforming it; but there may be other reasons that make this impossible even if you are alert. I discovered I had to add facets to make the edges work nicely, so any mapping would have been spoiled anyway.

Anyway, enough excuses.
If you try to map that as it is, there's no way to properly map the inset part. Here's an X axis cylindrical map of the sleeve. You can see that some positions on the map apply to two different facets - in other words, there's no way to apply separate mapping to both the inside and outside parts of the sleeve.
A cylindrical map with caps might seem better, but in fact the cap would be a separate area on the map, and difficult to integrate with the rest of the sleeve. Worse, there would also be a cap formed for the other end of the sleeve, where you don't want one. It could be sorted out by laboriously selecting vertices and moving stuff by hand, but that would be a nightmare. Who wants that hassle?

• A Solution

It occurred to me that perhaps if I could stretch the sleeve out into a shape which would map easily, I could apply that map to the original mesh. Here's how I did it.

In UVMapper Pro, select the part you want to map. In this case, it's a single sleeve. Now invert the selection, and delete, so that you have just the sleeve left. Take care to save this to a new filename!

Note that if the part you're working on isn't separated on the map, as it is here, it's useful to assign the selection you make to a region before deleting anything, and save the entire mesh with the region in it. This is because you'll need to be able to reselect this area exactly in a later step.
In your modeller, alter the mesh in whatever way is necessary to make it an easily mapped shape, as long as you only alter the vertex positions. Don't add to or take away from the mesh. Here, I've pulled the cuff part out from within the sleeve, and straightened out the puffy part.
Bring the altered sleeve into UVMapper and map it. A cylindrical map along the X axis, without caps, is right for this now. It also improves the mapping if you rotate the model around the Y axis beforehand, so that the major axis of the sleeve is as near as possible to the X axis. Export UVs for this part - there's no need to save the mapped mesh, but you may want to keep it in case you need to try different distortions.

Now re-open the original mesh in UVMapper. Select the part that you chose before, in this case the sleeve. Make sure you get exactly the same area of the mesh - if you assigned the work area to a UVMapper region, use Select > Select by > Region...

With the selection still active, import the UVs that you exported in the previous step, and the sleeve will magically take up the new mapping. You'll probably need to scale and move the selection to make it fit in nicely with the rest of your map.

• Another Example

Here's another example. The body of this same blouse model is cylindrically mapped, which works well for the most part - but the top surfaces of the shoulders are completely compressed on the map, making them impossible to texture accurately.
I separated the body in the same way as the sleeve example above, by deleting the rest of the mesh within UVMapper. Instead of using a modeller, this time I imported that into Poser and used the magnets to stretch out the upper portion. If you do this, be careful with the import and export dialogues; uncheck all the boxes on import, and check only "as morph target" when exporting.
I put a straight cylindrical map on that (in the Y axis this time), exported UVs, and imported them to the original as described above for the sleeve. Result, much improved mapping. It still isn't perfectly uniform, but with some work it could be further improved; and at least the texture isn't completely stretched out as it used to be.

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