Is It Worth Changing Distance/Length Units (Project Settings->Editor->Appearance) from cm to km for a large scale project (space for example)?
What are the pros and cons of changing the units? I can’t seem to find a clear answer other than the default is cm but I can’t find anyone talking about changing to km or the reasons for doing so.
I’ve been testing and it seems Unreal Engine can handle some big numbers… ridiculously big… 48309843029482093443 is a valid x position for example and, at first glance, it really doesn’t break anything (I’m sure there’s going to be some error when I dive deeper). I know the values become less accurate at large scales so switching to km would reduce this (I think).
I’m playing around with large-scale space simulations and wanting to push the scale as close to real-world as possible. I’ll be dealing with mostly planets, moons, stars, asteroids, etc. and the distances between them. I’d also like to add in smaller details like satellites, space stations, etc. I’m sure I’ll need some trickery with level streaming or world partition etc. to make it all work properly. This is all new territory for me and I’ve still got a lot to figure out but I’m mostly trying to figure out the issue of scale and units to begin with so that I’m starting from the right place.
Is there any other reason to switch the units? Why is it under Editor Appearance? Does it affect the physics and scale of my meshes? Does it break anything in blueprints or C++ classes? If I set UE units to km should I set my Blender units to km to match when creating a mesh? Is there anything else I should know about changing the scale?
Sorry for so many questions I’m just struggling to find any answers anywhere (if they’re out there please link cause my searches are coming up empty!). Thanks in advance for any help!
Changing the setting you mention will not do anything. None of this will help in UE4. You’ll run into floating point errors early on. You will get a stable simulation 2.5 km from the world origin, things decay fast after that. At 5km it gets really shaky. You can’t spawn actors further than 10km from world origin, or thereabout.
Try this, see what happens:
You generally fake things. Is the closest star really 150aus away? You tell the player it is, put a marker and a label on the screen → there, a star. They will not spend the next 400 years trying to get there. They’ll activate the hyperdrive and whatnot… But you probably do realise all that already.
You could scale your world down. Does the spaceship need to be 100m long? Perhaps 10m is fine, perhaps 1m is enough providing everything else is to-scale. The player won’t notice.
Now that everything is 100x smaller, you can have a space battle in a fake 250km radius. The universe map will not be the size of the universe, surely, it would be a model:
Also, look into large works and world shift origin:
