Problems with Overlapped UV Shells in 3D max

XzY

Hello everybody.
If in 3D  max forget to move the overlapped shells to UV and save the model(Photo 1), then when you reopen, the overlapped shells in UV will "merged" together and they cannot be selected separately + the cut lines on the model in the viewport will disappear or partially disappear (Photo 2).

I didn’t work at 3D max with UV therefore there were questions:

1. Is this normal?

2. What to do if the shells are so “merged”? Is there any way to fix this (except how to redeploy)?


Photo 1.

Photo 2.

srsface

I don't recall ever noticing that overlapping UV islands would get welded together on their own like that. Sounds quite odd!

Maybe a way to go around it would be to move the UVs of the other part 1 full unit to the next UV grid slot. That way the parts will still be using the same part of the texture, but they won't be overlapping in UV space anymore.

XzY

This is good advice. I usually do that. I transfer the overlapped one to another tile, as you said.
But sometimes you can forget to do it with one small piece on UV (And it will merge with the lower shells). And see this only when the texture is already done. And I don’t know how to fix this when it happened.

monster

This used to happen to me ages ago, usually after a weld operation. You can separate them by selecting the face geometry for one side in the viewport and in the UV Editor right click and select "Detach Edge Verts".

If you have only 1 object selected, with 1 unwrap modifier does this return false:

$.modifiers[#Unwrap_UVW].weldOnlyShared

(Open the Maxscript listener, select your object, paste, and hit enter.)

If it return false run this command and then go to Options | Save Current Setitngs As Defaults

$.modifiers[#Unwrap_UVW].weldOnlyShared = true

Weld Only Shared means only UV verts that share a geometry vert will be welded. It's considerably slower on million+ poly meshes. But you shouldn't notice a difference.

XzY

The problem appears only when exporting to OBG. For example, FBX works without problems. This is an export bug in OBJ. Everything works well if you uncheck the texture coord in Optimize. But I do not understand well what he is responsible for and what consequences may arise if it is removed.

monster

It's not a bug, it's a way to reduce data and file size.

I recommend not checking any Optimize options. That's like jpeg compressing your source photoshop files. 
If this is for a game then the game engine will optimize again on import, no need to double compress/optimize.

XzY

Thank. Now everything has become clear:)

I do not know the game engines so well. And I did not know that they optimize the file upon import. Then it really does not make sense to optimize the model also in 3D max.