How to unwrap grid-topology mesh without stretches?

Question

In a forum somebody stated that good UVs should be stretch free. I have therefore tried to make my UVs as stretch-free as possible:

Could somebody tell me if it is actually true that good UVs should not stretch? And if yes, could somebody tell me if my UV is actually (more or less) stretch-free or if I have misunderstood it what he meant by "stretch free"?

Thank you very much for the help!

Edit: Or is the second one better?

Edit2: Or this third one?

This is pretty much the best use of that available information that can be stored in the image.There is some stretching, however that is on the mesh side (how the texture is applied to the mesh). — J Sargent, Oct 16 '15 at 01:30
@NᴏᴠɪᴄᴇIɴDɪsɢᴜɪsᴇ Can you explain the "stretching on the mesh side", please? Do you mean that the dense areas in the mesh would not need so much space in the UV? — tmighty, Oct 16 '15 at 01:45
Basically the mesh is not a cube, yet is unwrapped with very consistent area for all faces. This just means that smaller faces will be able to have higher detail. Try adding a texture to your mesh, and you will see what i mean. — J Sargent, Oct 16 '15 at 01:48
@tmighty Remember, that you can easily check the stretch size of your UV island. After unwrapping, being in UV Editor window press N and check the STRETCH box in Display panel of the properties shelf. Blue color= no stretch, red color= 100% stretch. — Paul Gonet, Oct 16 '15 at 14:11

score 5 · Accepted Answer · edited Apr 13 '17 at 12:57

Since unwrapping is mapping a 3d surface onto a 2d plane, there are a limited number of ways to avoid stretching.

In general the more you avoid stretching, the more seams you will get. Note that stretching is not necessarily so bad as to attempt to avoid it entirely, while good to avoid extreme cases - baking, texture painting - etc, will compensate for subtle stretching so that its not such a problem. Unless you're painting onto the 2D image directly.

In the example of a 'vase' like object, (lathed 2d shape), you're likely be better off accepting some so pixels are aligned with the UV's (the third one, in your question). ... and not diagonally shared across faces which may look odd at low resolution/mipmaps).

UV unwrapping for games/realtime-engines is typically a trade-off between:

number of seams
distortion
maximum texture usage
avoid bleeding with low mipmaps
... and the time it takes you to create.

Whats good or not depends on your project.

Some ways to avoid stretching include:

Use Blenders Unwrap tool (and do some manual pinning of UV's).
Create a mesh out of flat surfaces and project each surface separately,
see: Smart Project which automates this.
For quad-dominant meshes a grid can unwrap neatly to UV space.
See Blender's Grid Unwrap tool (called Follow Active Quads in Blender).
The amount of stretching depends on how regular the surface is.
Unfold the mesh into UV-space (think of unfolding a paper-model), See the addon referenced here.
Note that unfolding may only be of limited use for UV-mapping since it tends to create a lot of seams and overlapping regions.
Its best suited to low-poly meshes.

May I ask you if you create game models? I am asking because it is still not clear to me what a great UV unwrap for the vase would look like. — tmighty, Oct 16 '15 at 09:28

score 1 · Answer 2 · answered Dec 18 '16 at 11:39

You can check your mapping for stretched areas through this nice check box, in the image/uv editor Press N for properties, then you'll find the Stretch check box as shown in the picture,choose Angle. It can also check for Area stretching, incase you model to scale.

How to unwrap grid-topology mesh without stretches?

2 Answers2