Whats the best way to detect the floors Y position below character?

I have though of ray-casting but i don't think its efficient having ray-casting for all of the players all over the place, i have also thought of creating a sensor object to detect floor but the floor isn't a separate part, its part of a big object.
So whats the most efficient or most common way of detecting floor?

Thanks.

 

Raycasting is most commonly used. Its a fairly generic solution.

Alternatively you can read the height directly from your terrain. This solution will vary depending on the exact implementation of your scene. But if you have supreme commander numbers of units around it can be worth the effort.

 

I know how to create ray-casts and get game objects through them but how to i detect which Y position it hits.

 

Read the docs.