Problem UV unwrapping: aspect ratios not kept

I’m having a problem with aspect ratios when UV Unwrapping a rectangular object (part of a house and balcony); been struggling with this for many hours now and finally decided to make a very simple test case to figure out what the problem is.

So now I created this simple bar, by taking a plane, extruding it twice in the y direction and then the whole thing in the x direction to create what is basically a straight, 3-part bar. It is easy to see how this could be unwrapped without distorting anything.

Based on various tutorials that I watched about UV Unwrapping I added some seems to where it should come apart, but failed to create a useful UV map as all the aspect ratios are terribly distorted, to the tune that there is no clear relation between the rectangles in the UV map and the rectangles of the original object.

If I’m using a single cube (such as the starting object when creating a new file), it’s all fine. The moment the object becomes slightly more complex it fails. I’ve no idea what I could possible be doing wrong here; it seems to me I’m doing the correct thing - but the result isn’t there. I found references to a related bug - but this appears to have been fixed some years ago already.

Any suggestions are highly appreciated!


uv _unwrap_failure.blend (507 KB)

Before unwrapping apply any non uniform scale that your object has with Ctrl+A. Sounds like you scaled the object in object mode rather then in edit mode so you didn’t keep the object scale constant. In your example the objects X and Y axis has a scale of 150 and the z axis a scale of 1. Apply the scale to give a scale of 1 for each axis

Unwrap after applying scale

Generally speaking when you use the U / Unwrap option, use the default ‘Angle Based’ unwrap method for organic objects and the ‘Conformal’ unwrap method for hard surface objects (try both to see which gives the better unwrap). Change the unwrap method with F6 or the options at the bottom of the toolshelf