Seams

Seams are the “borders” of an unwrapping operation. Remember the cube in Figure 8.1? When it’s unwrapped, the normal black continuous lines would be the seams. You can also think of seams in clothing; before a shirt is made, it’s just a series of flat pieces that are later joined into a three-dimensional garment by stitching them together at their seams. In 3D, the most popular unwrapping method is to use seams; first, you define the seams in the 3D model, and then the UVs are unfolded according to those seams.

What’s important to keep in mind with seams is that they’re not desirable. Seams are usually placed in areas where they’re less visible, and the reason is that when you apply a texture, in the seam area you’ll notice a “cut” in the texture. That happens because where you have a seam, it appears as a border on the UVs, which means that even though you make the texture continuous without any cuts, the size of the seams on one side or the other may not be exactly the same, causing the resolution of the image to change across that seam.

In UVs, the bigger a polygon is, the more resolution it requires in the image; thus, the texture displayed in the 3D model will be sharper. What’s important here is to know which parts of your model need more detail in the textures and will therefore need more space on the UVs.

In Figure 8.4, you can see the effects of seams and how the size of the UVs affects the projected texture.

Figure 8.4 While the two halves of the 3D plane (on the right side of the image) have the same size, the texture on the left side of the 3D plane has less resolution, which is an effect of that part of the UVs (on the left side of the image) being smaller.

In Figure 8.4, you can see how the size of the faces on the UVs (left side of the image) and in the actual 3D model (right side of the image) are independent, but the size on the UVs defines the resolution of the texture in the 3D model.