Class KX_SCA_ReplaceMeshActuator

SCA_ILogicBrick --+    
                  |    
      SCA_IActuator --+
                      |
                     KX_SCA_ReplaceMeshActuator

Edit Object actuator, in Replace Mesh mode.

       # Level-of-detail
       # Switch a game object's mesh based on its depth in the camera view.
       # +----------+     +-----------+     +-------------------------------------+
       # | Always   +-----+ Python    +-----+ Edit Object (Replace Mesh) LOD.Mesh |
       # +----------+     +-----------+     +-------------------------------------+
       import GameLogic

       # List detail meshes here
       # Mesh (name, near, far)
       # Meshes overlap so that they don't 'pop' when on the edge of the distance.
       meshes = ((".Hi", 0.0, -20.0),
                 (".Med", -15.0, -50.0),
                 (".Lo", -40.0, -100.0)
                 )
       
       co = GameLogic.getCurrentController()
       obj = co.getOwner()
       act = co.getActuator("LOD." + obj.getName())
       cam = GameLogic.getCurrentScene().active_camera
       
       def Depth(pos, plane):
               return pos[0]*plane[0] + pos[1]*plane[1] + pos[2]*plane[2] + plane[3]
       
       # Depth is negative and decreasing further from the camera
       depth = Depth(obj.position, cam.world_to_camera[2])
       
       newmesh = None
       curmesh = None
       # Find the lowest detail mesh for depth
       for mesh in meshes:
               if depth < mesh[1] and depth > mesh[2]:
                       newmesh = mesh
               if "ME" + obj.getName() + mesh[0] == act.getMesh():
                       curmesh = mesh
       
       if newmesh != None and "ME" + obj.getName() + newmesh[0] != act.getMesh():
               # The mesh is a different mesh - switch it.
               # Check the current mesh is not a better fit.
               if curmesh == None or curmesh[1] < depth or curmesh[2] > depth:
                       act.setMesh(obj.getName() + newmesh[0])
                       GameLogic.addActiveActuator(act, True)

Warning:

Replace mesh actuators will be ignored if at game start, the named mesh doesn't exist.

This will generate a warning in the console: