now ,I use player postion as coordinate origin point at init time, each squares length is 2*R,slipt map, use backtracking,try to found next destination in 8 direction and record the history postion ,if fond there have not load scene,refresh map...,it can success to explore the whole map and found the next level portal
the problem is inefficiently use this method,some one know a btter method,when refresh map!