I'm using Blender as a modeling tool for Unreal Engine 4. It usually works great, but when I import into Unreal it gives me a lightmap overlapping error. So, I ask, whats wrong with my lightmap?

Lightmap: Lightmap)

I have already aasked the Unreal forums to no avail. So how can I get these to work?


Packed island lightmap: enter image description here

Also the exact error is: "Lightmap UV are overlapping by %65.3. Please adjust content"

Packing the islands bulks the number from %28.5 to %65.3 overlap.

Had to delete the image of UV for textures becqause the exchange only currently allows me two links.


I have unpacked, which makes the problem worse and the scaling is correct.

EDIT EDIT EDIT: Do I add threads or remove them? How do i this? How do I unwrap uniquely? Thank all of you for your help so far.

  • 1
    $\begingroup$ Can you add the specific error text to your question please? ;) $\endgroup$ – Keith M Jan 22 '16 at 18:50
  • $\begingroup$ Did you try following steps from this thread ? If it says you "overlapping" did you try to check whether UVs aren't overlapping ? The easiest way - with all still selected Ctrl+P to pack islands. $\endgroup$ – Mr Zak Jan 22 '16 at 18:59
  • $\begingroup$ Packing the islasnds makes the problem worse; even if I adjust the margins of packing, it makes it worse. Ill add pics of the packed islands to my orgiinal post. $\endgroup$ – SirChenD Stroy Jan 22 '16 at 19:20
  • $\begingroup$ Is the scale applied to model ? Packing works not as expected in your case. Did you try to unwrap once more (you can create one more UV map only for testing) and packing after that ? $\endgroup$ – Mr Zak Jan 22 '16 at 19:47
  • $\begingroup$ Scaling is correct and I have tried unpacking, it doesn't makes error worse. $\endgroup$ – SirChenD Stroy Jan 22 '16 at 20:12

It looks like you have overlapping areas in the packed UV map. You can see these long diagonal streaks going in your layouts that intersect other UV faces. But it's hard to tell what's going on there without seeing the .blend.

One pointer is if you use N-gons in modeling make sure to convert them to quads and tris before using pack in UV editor because it seems to often screw the N-gons. You can find N-gons be selecting a quad face and finding faces with more polygon sides with SHIFT+G. You can triangulate them with CTRL+T and join back to quads what you can with ALT+J.

Smart UV project (also includes packing algorithm that seems to work) handles them fine, as well as unwrap and I guess it won't be long until pack itself will be fixed to handle them properly. I recommend just using the smart UV project (if you don't want to manually unwrap with seams that yields best results) to pack all of the object at once and generally making your levels out of smaller rather than larger sets of geometry.

Also please use margin around your islands. When the lightmaps are baked if you have light and dark areas very close to each other in the map they are going to bleed into eachothers areas as the map is sampled.


When you get that error it means that some areas of your UV map overlap each other, which makes the final color of the lightmap unreliable because those areas are both lit in a different way. These show up in the UV editor as a slightly more vivid orange color. You can also view the UV layout in UE4 by pressing the UV icon in the toolbar of the static mesh editor. To fix this you need to unwrap your lightmap UVs completely uniquely. Also, your UVs are going to need more padding and fewer seams to make good lightmaps. You should aim for four pixels of padding between islands and two pixels of padding around the edges of the UV space.

  • $\begingroup$ When you say unwrap the UVs uniquely what exactly do you mean? $\endgroup$ – SirChenD Stroy Jan 22 '16 at 20:28
  • $\begingroup$ Don't put any UVs over any other UVs for lightmaps. $\endgroup$ – Spencer Brown Jan 23 '16 at 23:30

It's actually quite hard to detect the problem without having the .blend to check or at least having a screenshot of the model, but seeing your packed screenshot I guess that you have either

  • connections between islands where there should be seams
  • or you haven't selected all islands/verts before you packed your islands
  • or both

Your Answer

