UV mapping for beginners by Cirstyn Bech-Yagher

[Carlosan]

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New to the world of UV mapping? We take you through the fundamentals of this critical 3D task.

Known as the most tedious task in 3D, especially for beginners, UV mapping is also the glue that binds models, bakes and textures together.

It's a crucial task, too, as a bad set of UVs and their resulting output can make even the best 3D models look awful. Whether you love or hate UVs, there's no escaping them – they are essential to understand.

 

UV space fundamentals

Try using a UV grid rather than a checker map – a UV grid will show a lot more issues, such as flipped polys

The reason why a UV map is the glue between model and textures is that it's not only the flattened and mapped topology of your model, it's also the basis for your map bakes.

This means you need to take your mapping into consideration as you model – bad UVs give bad bakes.

You can always tweak bad curvature, height or occlusion maps in Photoshop CC at a pinch, but bad normal or similar map output can be a real pain to fix if you don't keep them in mind from the get-go.

This means the first thing you need to know about UV mapping is what UV space is. Based on a 0 to 1 grid, with 0.5 as the middle coordinates, a UV map consists of your 3D model's XYZ coordinates flattened into 2D UVW space – or tile, as it's called.

Depending on your modeller and mapper, 3D's horizontal X-axis equals U in 2D space, vertical Y equals V, and the depth coordinate Z equals W. There is no madness to the letters, only method: 2D's UVW is used solely to avoid confusion with 3D's X, Y and Z. This equalling of coordinates is – to put it simply – how 3D space translates into flattened 2D space.

Make sure your mapped UV groups have sufficient gutters. Look for the Spacing settings in your UV mapper

You may be wondering why 2D space also has a depth coordinate. This is to make sure that no matter how you choose to map, flip or stack your UV'd bits and pieces – called islands or shells – the depth coordinate will ensure they show correctly in 3D no matter their mapping. 

It's also vital that all your model's flattened polys need to be inside the UV tile in order to provide your baker and renderer with accurate texture information.

Some renderers and texturing applications take this a step further by also providing support for something called UDIM – U-Dimension. In simple terms, UDIM makes UV mapping and texturing easier by enabling you to create multiple UV grids for the same model by allowing you to have 10 tiles on the U-axis, and an (almost) infinite amount on the V-axis. 

As with a normal UV tile, you can't have polys outside of the UDIM tiles' boundaries either, but we'll get to that later.

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