Do you lose UVW maps when you attach objects together? (pics inside)

I did a simple experiment tonight. I created two seperate boxes, UVW unwrapped them and imported them into Unreal Engine. Simple. - No problems.

Now when I attach one box to the other in 3DS max and import into Unreal, I was getting a light map UVW overlapping error. But now I’m not. However, I’m getting some lightmap errors on the texture.
So my question is: can you attach objects together after you’ve UVWunwrapped them seperately?

You can attach them, but UV now share same space. So if you blend your 2 pictures of uvw you will see that they are overlapping each other which is a big no-no for Lightmap.
Add another UVW unwrap modifier AFTER you attach them together and choose channel 2. Then rearrange uv shells in such way so they don’t overlap.

Hmm. So once I’ve attached one box to another - I’m left with a UVW unwrapping modifer already. And then I add another of top of that - set to channel 2 and re-arrange? Do I move the maps or abandon them?

That doesn’t seem to work at all. Here’s what I’ve found.

Three boxes.

Unwrap Box 1 - Done
Attach box 2 to box 1 - Then unwrap only box 2 while it’s attached to box 1 - Done
Attach Box 3 to box 2&1- Then unwrap box 3 while it’s attached - Done

This is the only way that’s working - because as soon as I attach something to an object - I lose it’s UVW mapping if I map it seperately.

I don’t understand this because If I have a complex object, how am I supposed to create seams on small objects hidden behind other objects. I can’t isolate!

You don’t have to think about all of it. Just merge everything together and THEN unwrap boxes in Channel 1. During importing in UE4 enable auto generation of UV for Lightmap

I don’t think you understand what I’m getting at. If I have an complex object that I need to create seams with, I can’t unwrap it without breaking it apart - can I?! And if i break it apart, UVW map it and then try to join it all back together again - I lose all that mapping.

When you attach objects, it does nothing to the UV’s they will be merged together. So if the UV’s are in the same space then they will be overlapping after you attach them together. To fix this, you need to apply a Unwrap UVW modifier, this will allow you to look at the UV channels and you can see if they are overlapping and then you can use Pack UV’s which will automatically rearrange the UV’s so that they don’t overlap.

Yes, you can. There is a host of rich UV unwrapping tools in 3ds Max, that lets you mark out seams, do pelt mapping, and a bunch of other things. Look at the “Unwrap UVW” modifier and search tutorials for each feature online (or read the manual – it actually explains how to use it, but not everyone learns well from text.)

So, typically, you’d model all the objects, and attach them all together, first. Then you’d apply a “Unwrap UVW” modifier, and texture map it in whatever way you want.

Also, make sure you understand the “Multi/Sub Material” in Max. When you have a single mesh, but need multiple materials, the multi/sub is “the” material, and each other material plugs into a slot in that; you then select material ID per face in the mesh.

I’ve tried that and it didn’t work. As soon as I attach one object to the other and put another UVW modifier on it and set it to channel 2, I have to unwrap one of the objects again.
I’ll show you what I mean in pics.

Two seperate boxes. Both with a UVW Unwrap on channel 2.

[SIZE=6]1. Blue box unwrapped[/SIZE]

2. Green Box Unwrapped

3.Attach green box to blue box - now they are one object and there’s still a UVW unwrap modifer left over in the stack on channel 2

4. Open the UVW unwrap and here is the map of one of my boxes and the other one is nowhere to be found. If I poly select all (ctrl + a) it only selects one box. So where’s the other unwrap gone?

You need to collapse the stack before attaching. The modifiers happen in order, bottom goes first, so if you go down to Editable Poly then whatever you do there applies before the modifier above it.
You can also drop an Edit Poly modifier above the Unwrap UVW modifier and then attach there.

Ohhhhh. That’s where I’m going wrong. So collapse first.
You’re a bloddy legend mate. :smiley: :smiley: :smiley:

! Could you please make me a favor listing the exact steps you followed to achieve that? I’m trying to do the same but my UV’s are getting messy every time I attach the items