Help with stretching UV's

So i unwrapped a whole bunch of objects and gave it the 1024x1024 ‘UV grid’ texture so i can fix any possible stretching. Now i want to swap out the UV grid with different textures (for different models) but all the UV’s are stretching to conform to the new aspect ratio (of the new images). The only way around it is to re-uv EVERYTHING, this time using a different UV grid for different object, 1 that matches the right size of the corresponding maps. Can anyone suggest a different method (instead of re-uv-ing) or perhaps i made a mistake somewhere in understanding blenders logic. Any help will be greatly appreciated.

Why not just scale the existing UVs to correct for the change in aspect ratio? E.g. if you unwrapped on 1024x1024 (1:1), and you now want to use an image that’s 1440x480 (3:1) without changing the aspect ratio of the unwrap, then scale down in the X-direction by a factor 3 (SX/3). Of course, you end up only using part of the new image.

Best wishes,
Matthew

I considered scaling the UV’s to match the new aspect ratio, but to go in and scale for each object(about 50)??? Quite a headache! Also, if I scale without the UV grid, i might be scaling too much or too little, so I’d have to create new grids for each object. I thought maybe i was doing something wrong like all i needed to do was check a check-box to keep consistent ratio regardless of changing/swapping the maps. Anyway thanks for replying.

I didn’t realise you had that many separate objects. You could join them into one, do the UV rescaling, and split them again - but then you’d have to rename them all. Or you could use a script.

Quite a headache! Also, if I scale without the UV grid, i might be scaling too much or too little, so I’d have to create new grids for each object.

You might be, but you shouldn’t be. The rescaling is completely determined by the aspect ratio of the new image; no need to create another grid.

Best wishes,
Matthew

Re-naming isn’t a problem ('cos i didn’t name them in the first place!). I’ll Just attach them to a single object and separate them afterwards! Thanks for you help. I’m kinda new to blender and still getting use to its logic. Though the problem does seem more like a bug - can’t imagine when you’d want the UV’s to change its aspect ratio. Anyway thanks again for your help.

Have you looked at 33055?

It’s exactly the problem Andrew Price described. The developers diagnosed a different bug and dismissed Andrews claim about the UV’s automatically changing aspect ratio each time a different map is assigned (with a different aspect ratio). I don’t think they even put it in the to-do list. For now I’ll attach everything to a single object. For future reference, ONLY USE aspect ratio of 1:1 maps. Thanks for the heads-up though, I can see this problem wont change any time soon.

What do you think about a coordinated squeaky wheel campaign to squash this bug? I found at least 5 people recently on this website without trying, 3 in IRC when I happened to pop in.

I wouldn’t know where to start, somewhat new to blender! Though the bug has to be squashed. What’s IRC?