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I'm having problems using the UV mapping in blender 2.67. Specifically, I am trying to unwrap a really simple mesh, but the UV map is still giving me a net where some of the boxes are completely out of proportion to the others, which causes the texture to stretch horribly. Here is a picture to illustrate:

Mesh on left gives UV map on right

The mesh only has those three faces you can see in the picture, and the single seam on the front corner. It's a trivially simple mesh, so I really don't understand why the two side faces are being stretched in the UV map to be the same size as the top face. I've tried clicking the average islands scale button as suggested by some of the answers to other questions but that has no effect. It's frustrating because it seems so simple.

Hopefully someone can show me the presumably simple mistake I am making!

Edit: Just to make this clearer, I have already added a seam as the first answer suggests i do. Hopefully this picture will make that clearer, the yellow arrow is pointing to the edge i seamed. The mesh is only three faces so should only need this single seam. The image shows the mesh from infront and behind/underneath so it should make more sense.

Left shows looking from infront/above, right shows looking from behind/beneath

Double Edit: One more picture for clarity on the seam issue. The mesh is unfolding correctly, it is just the scale of the unfolded map that is incorrect (in relation to one another)

enter image description here

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did you mark seams? –  Vader Mar 22 at 18:40
    
Yeah i did. It's only three faces so i marked a single seam on that front edge you can see in the picture (red) as i mentioned ^^. Without seams it produces a weird skewed net of trapeziums. –  user3049527 Mar 22 at 18:51
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1 Answer 1

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If you scaled you box in Object mode you will need to apply the scale to get the faces the right size. To apply the scale Ctrl A -> Scale

You need to add seams to properly unwrap your mesh. If you do not use seam and try to unwrap you will get a weird and distorted UV map. To add a seam you can select and edge Ctrl E -> Mark Seams.

enter image description here

After you add enough seems to cleanly separate faces in the correct places you can unwrap the mesh, U -> Unwrap. Make sure you select all polygons before unwrapping.

enter image description here

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I do have a seam in place already though, it is red in the first screenshot. I have edited the top post to explain. Note that the mesh is not a full box, only three faces of one. The three faces visible in the first screenshot are all the three faces of the mesh. –  user3049527 Mar 22 at 19:06
    
@user3049527 a single seam is not going to make a difference. you need to add more. Image you were trying to create a paper cutout of the box. Would a single cut at the edge allow you to unfold the box? –  Vader Mar 22 at 19:07
    
Yes it would in this case as it's not a full box, its only three faces. –  user3049527 Mar 22 at 19:12
    
@user3049527 I updated my answer –  Vader Mar 22 at 19:17
    
Ah excellent it was the ctrl-A -> scale that did it. Still not quite sure what was happening though - What is the exact function of that scale modification? I went back to object mode to apply it then re-un-wrapped the mesh in edit mode which fixed the problem instantly. Thank you very much for your help :) –  user3049527 Mar 22 at 19:31
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