subdivide
Returns the four children formed by subdividing this tile. This tile's sector is subdivided into four quadrants as follows: Southwest; Southeast; Northwest; Northeast. A new tile is then constructed for each quadrant and configured with the next level within this tile's LevelSet and its corresponding row and column within that level. This returns null if this tile's level is the last level within its LevelSet.
Return
an array containing the four child tiles, or null if this tile's level is the last level
Parameters
tile
the tile factory to use to create the children