A node builder is a WAD authoring tool. The VERTEXES, LINEDEFS, SIDEDEFS, and SECTORS lumps fully describe the structure of a map, and it is relatively straightforward for a level editor to create them. However, for rapid rendering and game simulation, the Doom engine needs information on how these structures interrelate. Most time-consuming is the creation of a binary space partition of the map. The node builder used by id Software is called idBSP.