Prevent items/player from going through walls/floor

[system]

There’s this online game, Asheron’s Call, I’m not sure if I can say the name of it here (??) so sorry if not. Basicaly no matter how hard you try, you can’t go through the walls, you can’t glitch through or anything and I was wondering if there’s a way to make a Unity3d game like that? AC works with “landblocks” and if your character runs into a landblock area that’s missing or crashed then you lag out and disconnect, and the game can’t save your character there so it reloads you back where it last saved you, although this was a problem in AC before, because it allowed duplicating of items when abused, I still liked that you couldn’t fall through walls or the floor no matter how hard you tried. In Unity3d you’d fall forever unless there’s a fallout script.

I understand they used a different engine, but just curious if something similar is possible in Unity. I’d like to prevent the possibility of falling through, no matter the velocity, size, gravity, or mass of the object.

maybe a script even, like a fallout script but instead of a total reset or death it detects the character/object going through the floor and sets to nearest x,y,z above terrain/within gaming boundaries. that way as soon as the object even thinks about going through, it’s instantly reset to the correct side of the wall/floor

I am no good at scripting yet so let me know

[save]

I'd update a `Vector3` variable once a second or so when the player is grounded.

var currentGroundPos : Vector3;

function Start () {
    InvokeRepeating("CheckPos", 0, 1);
}

function CheckPos () {
    if (grounded) {
        currentGroundPos = transform.position;
    }
}

To check if something is grounded you can either use the `CharacterController` variable `isGrounded`, collision detection or use a raycast, have a look at Aldonaletto's answer.

When the player falls below the ground you relocate the player, which would be like this for an example:

var player : GameObject;
var lowestGround : int = -10;
if (player.tranform.position.y < lowestGround) {
    player.transform.position = currentGroundPos;
}

Using this method you could also check if the player is grounded before you save your game.