I’ve tried applying both Lit and Unlit materials to these meshes (the buildings) I’ve imported into my level alongside the Google Photoreal tileset of San Francisco, and in both cases I end up with glowing buildings, relative to a dark terrain, at dawn and dusk. This is my first UE and first Cesium project, so I’m not sure if this is something commonly encountered and easy to fix with a couple checkboxes, or if I’m just doing something really weird.
It almost looks like the Cesium tileset is not affected by the Cesium SunSky Directional Light (which is expected, since it’s unlit), but then when I apply an unlit material to the buildings, they still do not match the lighting condition of the terrain tiles.
Another idea I had is that materials applied to the buildings need to have a lower emissive strength when the sky is dark… maybe they look like they’re glowing because they’re actually glowing? But, I don’t know how to vary the emissive strength relative to the brightness of the SunSky Directional Light. This might explain why the buildings look relatively normal during the day, but glow weirdly at night.
If you have any ideas, I’ll try them all! Please help me out.
Images below shows Unlit dusk time where you can see the weird glow.
Using UE 5.2 and latest version of Cesium.
Thank you,
J
Hi @PCA_ejm, welcome to the community!
I’m not too sure what’s happening, and would probably need more details of your model and import process to have a guess. But I can provide some details of how the Google Photorealistic 3D Tiles unlit rendering works, in case it gives you a hint.
For an “unlit” tileset like GP3DT, we don’t actually use an Unreal unlit material. There are multiple reasons for that, but one big one is exactly the problem you mentioned: how do we set the emissive strength correctly in a scene that can (by design) have wildly varying lighting conditions? If there’s a solution to that, I don’t know what it is.
So instead, we render unlit tilesets with the same material we use to render lit ones. However, for unlit tilesets, we set the normal of every vertex to match the ellipsoid surface normal at that location, rather than computing a normal based on the geometry. In other words, the normal always faces “up”, away from the globe. This means that the side of the globe facing the sun (directional light) will be lit, while the back side will be dark. But the side of a building facing the sun won’t be any brighter than the side facing away (shadows aside, if there are any). We believe this matches the intention of the KHR_materials_unlit glTF extension while integrating more neatly into most Unreal engine applications.
