I found that it is still difficult to identify unambiguously the boundary of gyroidal graphitic structure (GGS) if I don't pay attention to each unit cell carefully from the beginning. So I decided to use the original strategy Chern used to build this structure with helical strips. The photos below show a structure consisting of two unit cells.
In the following photo, I show part of the gyroidal structure that contains only two helical strips. It is interesting to note that one helical strip is right handed and the other one is left handed. But this two-strip unit is still chiral because one of these two strips has to be shifted a half pitch w.r.t. the other strip in order to join them together.