text: The orientation of a glide plane is given by the position of the symbol in the Hermann–Mauguin designation, just as with mirror planes.
  They are noted by a, b, or c depending on which axis (direction) the glide is along. There is also the n glide, which is a glide along the half of a diagonal of a face, and the d glide, which is along a quarter of either a face or space diagonal of the unit cell. The d glide is often called the diamond glide plane as it features in the diamond structure. In cases where there are two possibilities among a, b, and c (such as a or b), the letter e is used. (In these cases, centering entails that both glides occur.) To summarize:
  * a, b, or c glide translation along half the lattice vector of this face.
  * n glide translation along half a face diagonal.
  * d glide planes with translation along a quarter of a face diagonal or of a space diagonal.
  * e two glides with the same glide plane and translation along two (different) half-lattice vectors.