Another terrain question

D4N005H

Hello there.
I am investigating popular games to learn about making a city (so that I can make a city for my own game project). Here there are two things in the scene, a mesh that has a texture of ground and the terrain itself:

So, my first thought was that the mesh is on the terrain (something like "decals") and it seemed to be true, because I've found some "errors" in the terrain of this game (see the image below)

in the image, it does appear that the grass mesh is on the terrain.
But apparently I was wrong, it seems sometimes there is no terrain at all!! and there is just a mesh! see the images below:

My question is, is it really that much matter if I don't "remove" or "delete" the parts of a terrain which are under meshes? does it really affect performance? Why do you think TestDrive Unlimited 2 developers did that (apart from higher RAM consumption (I guess)) ?

kurt_hectic

Like 10 years ago I remember a giant  box under the level I had to delete because of the performance issues, but I have no idea how it works nowadays.
My question is why you want to keep some mess? Keep it clean, cut everything what isn't visible.

D4N005H

kurt_hectic said:

Like 10 years ago I remember a giant  box under the level I had to delete because of the performance issues, but I have no idea how it works nowadays.
My question is why you want to keep some mess? Keep it clean, cut everything what isn't visible.

Good question, as far as I know, I can only make a terrain in Unity3D in a shape of square or rectangle, but the areas that I am talking about are not really rectangle or square, see the image below for more details:

So according to this, I am unable to "cut" the terrain or there might be another way to do so which I'm not aware of. So that's why I am a bit worried about it and now I'm even more worried after reading your message because the terrain is huge (it consists of 510 tiles of 2KMx2KM terrains which all of them together makes the huge terrain) and I don't know what should I do for the problem... .

D4N005H

correct me if I'm wrong, maybe making smaller tiles of the terrain does the job (something like the image below) but that I think would take a looong time... 

According to the information, what would you do if you were me for creating those parts of the city?
EDIT: I've searched the Net and found out that terrains in Unity3D are not able to be cut, so seems I can't do this. However I'm too worried about the performance, and the way I described in this post as I mentioned earlier takes too much time... so really don't know what to do now.

Eric Chadwick

If you have a terrain mesh, usually it's under all the other meshes. The errors you see above are probably from using a multi-tile terrain system, but doing a terrible job with the seams between them.

D4N005H

Eric Chadwick said:

If you have a terrain mesh, usually it's under all the other meshes.

Um...so do you mean that I should not worry about performance and not to cut the terrain parts that player won't see? then okay. Fortunately that would be a good news. Thanks.

kurt_hectic

Aha, so we are talking about height map combined with standard mesh. If you will keep some reasonable resolution of height map, it should be a huge deal; besides, if you can't cut off this spot you have no other options, right?

D4N005H

kurt_hectic said:

Aha, so we are talking about height map combined with standard mesh. If you will keep some reasonable resolution of height map, it should be a huge deal; besides, if you can't cut off this spot you have no other options, right?

Yes exactly, the resolution is not more than 513 maybe I'd use 1025 when needed but not more than that, ... and yep that is it.
Thanks for the replies, people.

Eric Chadwick

There are ways to cut out terrain in Unity, but the cutout might cost more in performance than it is worth.
http://wiki.unity3d.com/index.php/TerrainTransparency

If you use multiple terrain tiles (one heightmap per tile) then you can use Occlusion Culling to improve performance. http://docs.unity3d.com/Manual/OcclusionCulling.html

D4N005H

Eric Chadwick said:

There are ways to cut out terrain in Unity, but the cutout might cost more in performance than it is worth.
http://wiki.unity3d.com/index.php/TerrainTransparency

If you use multiple terrain tiles (one heightmap per tile) then you can use Occlusion Culling to improve performance. http://docs.unity3d.com/Manual/OcclusionCulling.html

Aha, thank you for the information. Specially the "TerrainTransparency" one, haven't heard of it before.