Since 1.5, Foundation allows to mod Custom component and links it to a fbx (see Exemple02)

The following LUA code computes and returns the global Y elevation of water from a global position:

  function MY_CUSTOM_COMPONENT:computeWaterElevation(_globalPosition)
      local raycastResult = {}
   
      -- Raycast from the _globalPosition + 1000
      -- to _globalPosition - 1000
      -- only on objects with a WATER flag
      local FromPosition = { _globalPosition[1], _globalPosition[2]+1000, _globalPosition[3] }
      local ToPosition = { _globalPosition[1], _globalPosition[2]-1000, _globalPosition[3] }
      if not self:getLevel():rayCast(FromPosition,
                                     ToPosition,
                                     raycastResult,
                                     2 ^ OBJECT_FLAG.WATER:toNumber())
      then
          MyMod:logWarning("MY_CUSTOM_COMPONENT: Water not found on the vertical of "
                        .. tostring(_globalPosition))
          return _globalPosition[2]
      else
          return raycastResult["Position"][2]
      end
  end

You can do the same with the ground by replacing OBJECT_FLAG.WATER by OBJECT_FLAG.GROUND

If the water (or the ground) is not found (for instance when the _globalPosition out of the map) then a warning is edited in the logs, and the code return the Y of the _globalPosition.