Modeling - Intro to UVs
Introduction to UVs
What is a UV?
A UV is a mapping of 3D space to a flat, 2D image.
All models have a UV, and they're used to place texture/material details onto our models.
While 3D software tries its best to auto-create these UVs, they usually don't do a very good job, hence we as artists usually have to manually go in and correct the UVs for later use in the pipeline.
The best way to think of it is almost like the wrapping for a real-life gift, or the outer fabric of a real-life plushie. To make a plushie, we cut out some kind of pattern of fabric, and then sew it together to make a real-life 3-dimensional shape.
For an example, see the attached video.
A UV is similar to this fabric pattern, only it's the digital equivalent for our models.
In most 3D software, the analogy from UVs to plushies is taken to the next level.
Generally, the software has us cut and define "seams" in our textures. These "seams" always follow along the edge lines that exist within our model. So to an extent, we can start planning for UV's as we're modeling our objects.
Basics of the UV Process
In the most simplistic implementation, most software make this process really easy. At least at the beginner level.
In short, most software that allows UV editing (see UVs in Maya or UVs in Blender) will have a separate "UV screen".
From this "UV screen", there will generally be a basic "automatic" or "smart UV project" button.
Generally speaking, hitting this button will have the software try to unwrap your model and reorganize the UVs, with minimal further input from the user.
The drawback of above is that any automatic seams are most likely placed in less than ideal positions. Some software has downloadable addons which will do a better job, but generally the default software unwrap doesn't really understand where to place the seams.
Seam placement matters because it tends to create visible lines and artefacts in texturing. So generally speaking, seams should be placed on the underside of objects, or along edges of the model, or otherwise at parts where texture deformities won't be noticed. Which the "auto" button doesn't always know how to do.