Yes, you can. In every type of mapping in max you can set a map channel (index). You can have as many as you want (well haven´t tried if there is a limit in the UE engine). I usually use channel 1 for my diffuse textures and set my unwrapping for the lightmaps to channel 2. In UE the channels start at 0. So channel 1 in max is channel 0 in UE and channel 2 in max is channel 1 in UE. When importing the fbx I turn the "generate lightmap UVs"option off, so no further channel is created on import. If you import that way the imported mesh will have the option generate lightmap uvs off and the default channel for lightmaps is 1 wich is channel 2 in max. So like this you can have whatever coordinates you want for your diffuse map default set to 0 and have the model to automatically use your unwrapped coordinates wich you created in max as channel 2. Bit confusing I know but i works pretty nice that way. Now if you need even more coordinates every further coordinate i set to 3, 4 or beyond in max. In the “Texture coordinate” node in the UE material editor you can set whatever UV coordinate index you want.
Of course you can set you unwrapped lightmap coordinates to any possible coordinate channel or index (it´s the same). But if they are not channel 2 in max you´ll have to manually change the channel of each imported fbx in UE. One little thing. If you have an uwrapper set to channel 2 make sure a channel one exists somehow even if you don´t need it. Otherwise channel 2 is not present when importing to UE.
Regarding your second question. Well it depends. It´s easier to unwrap if you split it up. But in general you can get the same result when keeping just one object. I for my part would split up the mesh in max by element. Unwrap each seperately. Attach all parts together again. Add another unwrapper on the assembled mesh and use this one to layout the different coordinates (by id) before exporting it to UE. On the other hand bringing a mesh over in pieces gives you the advantages to set the size of the Lightmap for each object seperately. Many smaller lightmaps are probabely better than one huge in case you need really huge lightmaps. Anyway I would go with a single mesh it ´s easier to handle .
Sorry I think I was misunderstood: I knew about the channels, what I wanted to know was if the seams I set on a static mesh on channel 1 (for example) can be set different on channel 2 without losing the ones on the first channel! and for seams I mean these ones
Surely your idea of peltmap all apart and, only at the end, attach all together is interesting! I’ll try it!
