UV unwrap proportions

This thing has been confusing me for a long time now… I have a workflow like this (modeling a house):

  1. Create a house texture in Photoshop with the canvas size of 2048x2048. The actual house image inside the canvas is usually a bit smaller and not necessary a square shape.
  2. Take this image in Blender as a BG image and model the house in front view based on the image. This results in a mesh that is not a perfect square (since the image of the house wasn’t a square either).
  3. Select the front face of the mesh and UV-unwrap. This is where I get confused: even though the mesh I’m unwrapping is not a square, it travels to the UV/image editor as a perfect square. In other words the proportions are wrong. When I load in my house texture into the UV/image editor, it doesn’t line up with the uv-face anymore because of this.

My question is, why does Blender change the aspect ratio of a face when it puts it in the UV/image editor? Is there something I can do to get the right proportions back so that I can just load my 2048x2048 texture into the UV/image editor and have it immediately line up?

Is there any workflow in which I can be sure my image automatically lines up in the UV/image editor (if I modeled the mesh based on that same image)?

Selecting “Smart Unwrap” will help. But you usually have to edit the faces when you get them unwrapped because it will unwrap the faces in proportion but lay them out differently. So go in and use the UV editor to move them around and line them up right.

Also marking seams will help but for what you want to do smart unwrap is probably better.

Now I don’t know what you are trying to do exactly. But work flow wise you would not normally map the reference image to the object. But rather have other images you map to the object that collectively make the maps or unwrap the object and then paint them in either in Blender or in a paint program. Another method is to map the object in Blender with several images and then bake all the image to a final image to the UV map for image space economy.

Thanks for helping!

My workflow is like this:
-Create a hand drawn front view of a house (with alpha transparency at windows)
-Create a 3D model based on that hand drawing
-Attach the hand drawn image as a texture on the 3D model

The point in this is that I’m trying to create a hand drawn feel to my scene which is why I decided to try to create my mesh based on the 2D drawing and not the other way around.

Is there any workflow tips that would allow exact placement of the UV texture (without having to manually try to align it)?

Not sure what the model is like but you could try project from view. It will overlap anything that has depth but it will hold the shape of the house. Could also try that in sections at a time if they over lap.