Questions about LOD and LOD Blending

Hello UE4 Forum,

I’m building a rather large map about 5km2 of a hill and a town below it. I’ve been told in this scenario that its best to sculpt it and create several LODs of the entire landscape sculpt and import it into UE4.

I’m a bit curious though, from what I understand LOD’s will be at its highest detail when the player and camera is closest to it. Since the Terrain is one huge mesh and the player will always be on it. Wouldn’t it always be on the highest LOD across the mesh? Or is there some way to only load the highest detailed version of the mesh to the immediate area of the player only and what is visible by him. And the rest of the area will load the lowest LOD or lower detailed LODs?

I was actually planning to sculpt the land scape in the terrain editor in UE4 but apparently its a bad practice?

Also does the in built automatic LOD system have a blending option I can’t really seem to find it or is it exclusively a possibility from the simplygon plugin?

Terrain isn’t one giant mesh. Large worlds usually consist of sublevels, and only few sublevels around the player are loaded. Rest of the levels, that are far away, are displayed with LODs, where usually a level LOD mesh is a single low resolution mesh, that represents both landscape, and whatever may be on it. In UE4 it is called World Composition.

No, sculpting terrain in editor was never a bad practice, just a particular workflow.

Hey Death Rey thanks for clearing it up! In that sense I could sculpt terrain in editor with World Composition as well and let the engine handle the LOD of its general terrain?

Alternatively I suppose its also possible for me to do a fully detailed sculpt in zbrush and break it apart to different sections and generate the LOD for each piece as sub levels depending on where the player is located.

When you use the Terrain editing tools you can Edit the view distance of the sub division of the terrain. I made this mistake of making the world all in huge chunk with out tinkering with this system and ran out of Memory! select your terrain and look in the Details panel you should find something in there that will adjust the LOD distancing of the terrain.

Additionally, if you’re wanting to sculpt in Zbrush (because last I checked UE4’s landscape tools don’t use pen pressure and aren’t tablet friendly) you can always bake your sculpt into a heightmap and UE4 will use that to generate the landscape.

Other than that - UE4’s landscape tool (and World Composition) are very efficient / optimized. I’d only ever avoid using them if you’re going for something low-fidelity (not a lot of verts) + handcrafted UVs and textures. And even then I’d 100% suggest breaking up the landscape into sub-pieces based on distance / frustum culling (what the user can’t see doesn’t need to be drawn, but if even a sliver of that mesh is visible the entire thing gets drawn) UNLESS it’s SUPER low verts - Draw Calls may genuinely make it so that there’s never a time when that would save you frame time.

Basically, on most GPUs a draw call is so expensive that by comparison ~ 5k - 15k Triangles are utterly free. As in, any less than that and you’re not even affecting anything. No discernible difference. So if your entire landscape is within that range it may be worth double checking whether or not what I’ve said is true (especially for your target min-spec or w/e) - not that I’d lie :stuck_out_tongue: it’s just that this is a “magic number” and as such it changes based on what you’re targeting - especially if that something is a device without a dedicated GPU. As far as I can tell those things are black boxes and the only way to know for certain is to test on them.