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.