In addition to modelling, we’ve also been tasked with UV mapping some of our models.
I haven’t had much experience with UV mapping in the past, so I thought it would be necessary to brush up on some of the basic theory revolving around UV mapping.
I found a nice article by Renier Banninga, (found Here) in which he goes over some useful tips and methods to use when UV mapping. In addition Digital Tutors also had some really useful tutorials addressing UV Mapping. (found here).
The Rengier article dives straight into the technical aspects involved in the UV mapping process, whereas in contrast, the Digital Tutors tutorial starts off by explaining some the basic theory and terminology used and then gradually builds into some of the more technical aspects of the UV mapping process. Both are great sources of information regarding the topic at hand and often include visual examples of what they’re trying to explain which I find incredibly useful being somewhat of a visual learner.
What Is UV Mapping?
UV mapping is a solution addressing the problem one may face trying to apply a two dimensional texture onto a model or piece of geometry that exists in a three dimensional space.
UV’s act as a bridge between 2D and 3D, allowing us to apply a 2D image onto a 3D object. Each face on the polygonal object is tied to a face on a UV map.
In reference to the image above: I like to think of a UV Map as a the 3D object stretched out and flattened, making it easier for us to paint on it and this process is often referred to as laying out the UV’s. (UV mapping)
When mapping our UV’s there’s a few things we need to keep in mind:
- UV’s need to be spaced evenly to work well, otherwise this could lead to our texture being distorted when applied to an object.
- Seams, , non-connected, non continuous edges on a piece of geometry, plan where they can be hide on an object.
Mapping Types And Their Uses:
Renier describes planar mapping as the most basic of the mapping modifiers to apply to objects.
It projects the texture onto a model from one direction and is useful for mapping objects like walls and basic terrain. however, isn’t considered to be effective when a complex object with many overlapping surfaces needs to be mapped
The reason for this being that it will often stretch the polygons that don’t face the projected map directly.
-An example of Planar mapping above-
Projects the texture in a radial pattern inwards making it very useful for mapping objects like tree trunks, arms, torso and legs. It’s very handy for blocking out mapping on various types of meshes. However it still requires a lot of tweaking afterwards in the UV editor.
-An example of Cylindrical mapping above-
Projects the texture in a spherical pattern onto an object. However it causes a very high pixel density at the poles of an objects mapping. This causes a pinching effect that’s hard to counter when painting the texture.
-An example of Spherical mapping above-
Pixel Density and Stretching
Try to keep your mapping a consistent aspect ratio for the pixel size in the texture map. Lookout for areas where the texture gets stretched or skewed. This can cause unnecessary problems for the texture artist who would have to counter any warped mapping.
To Minimize Seams when UV mapping, Simply align the vertices of the seam with the corresponding connection in the mapping on either the horizontal or vertical plane of the texture coordinates. This way the pixels align on one of the axes.
For technical objects, it’s easier to get away with seams since they tend to be quite fragmented, and the nature of the object allows it. however for organic meshes.
We can minimize the amount of seams as much as possible by using accurate, continuous mapping.
Banninga, continues by covering some of the more advanced aspects of UV mapping.
Optimizing UV Layouts
Optimized UV layouts are particularly useful for real-time characters.
(He’s basically stating to not waste space in your UV editor, and this is because the entire texture gets loaded into memory, so take advantage of it)
To do so, you should scale, rotate and move those UV-mapped vertices until no more space can be saved.
Unfolding and Relaxing UV’s
Unfolding and relaxing UV’s is a handy thing to do if your UV’s are caught up and tangled.
Inside the Relax UV option box we can edit some values such as Pin selected UVs or Pin Unselected UVs.
Pining either means they wont be affected the the action of the Relax UV’s
Relaxing with even and smooth out some of the irregularities in you’re UV’s.
Lets you unwrap the UV mesh for a polygonal object while trying to ensure that the UVs do not overlap. Unfolding UVs helps to minimize the distortion of texture maps on organic polygon meshes by optimizing the position of the UV coordinates so they more closely reflect the original polygon mesh.
Within the Unfold options we can set restraints, in order to achieve the effect we want, like limiting the unfold to only unfold Uv’s horizontally or vertically.