This topic has been done to death, but i have been unable to find the right answer. I have a scene as follows:
It has a bunch of modular wall pieces that have been put together in blueprints. The scene is then composed using the blueprints. Pretty simple.
However im getting some weirdness with the lightmaps! I have 3 uv channels; the first and third for some tiling stuff, and the second (UV1) for the lightmaps. In maya i just fill it in with some dummy UVs, and in UE4 im generating the lightmap UVs to overwrite it.
Now everything seems good until i bake. I get both overlapping and wrapping UVs even though i have succefully generated a correct non-overlapping set.
In UE4, it’s important to make sure your ‘minimum lightmap resolution’ is set correctly. if you have a relatively high-resolution mesh with lots of UV seams then the lightmap build tool is still going to try and put 3 pixels between your islands, making some islands smaller than 1 pixel in some extreme cases (which causes the ‘overlapping UVs’ error) and is probably why they are wrapping too, as the build tool runs out of UV space to put all the islands.
Try visualising your Channel 1 UVs to see if the islands are smaller than the spaces between them.