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blender 2nd uv creation for clean lightmap baking in unreal(lightmap issues)

HI there ,
i am having and issue in making lightmap uvs in blender for unreal in order to get perfect baking what should i do? i know how to do it i have read whole documentation and even from the world of level design source but i am unable to do it in blender the thing is there is no way to chance grid size of uv map in blender so that i can snap all the vertices to the grid points i will be providing files from blender u can check it out to know what i am doing worng i want clean results and my aim is to get perfect GLOBAL ILLUMINATION in unreal so here is are some pics. I would be greatfull if some one can make a grid picture in photoshop so that use that in blender so that i can snap the mesh vertices to the grid points to match it with unreal 64 , 128 , and so on light map resolution. Oh i wish i could change the grid size like people do in max so easily please if u can help me i would be grateful to you.

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here is the link for the file i am providing 3 file one is of blender ofcourse and 2 are in different formats fbx and obj you can download it from here.

and do tell me if i am doing some thing wrong.

The lightmap of the cube is ok, even though it is wasting quite a bit of memory, and indeed I don’t see artifacts on the cube itself. Is the object below the cube in the screenshot a single big cube or multiple ones?

devel.bmad i made a single cube in blender than export it to unreal made duplicate of it to work as a modular asset , so the image posted here it contains allot of mesh which is done by duplication of the single model

So, the problem is definitely not the UV unwrap, which is correct. Generally when you have large surfaces with a single light colour (like the floor below the cube) it’s better to use a single object rather than multiple ones because it’s easy that the seams among different objects get visible (don’t know the technical reason).
Are you building the lighting in production mode?

yes i was not on production mode thanks it helped but again even after production mode the seams are visible yes it helped alot and i wanted to make modular assets like for example:- if i want to make walls i will make a single cube and if i wanted to change the length i would duplicate it as for how much i will need to make it broad, well these are the results after the production mode.still getting seams with the multiple mesh and yes if there is a single mesh used for the floor clean result can be acheived with that but iwant to make it modular :frowning:
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You can do modular, just not modular completely flat clean surfaces. Game art is all about working and planning around limitations. Put an intentional seam at the end of modular bits along with a texture, and you’ll never notice the lighting seam. Or put in a normal map of tiles that breaks up the flat surfaces. Or use bigger moduler pieces. Or use meshes to cover over the seams.