Line group

For convenience, the fractions are scaled to the size of the repeat; they are thus within the line's unit cell segment.

They are the infinite limits of the discrete two-dimensional point groups Cn and Dn: There are 7 frieze groups, which involve reflections along the line, reflections perpendicular to the line, and 180° rotations in the two dimensions.

Each appearance has a different orientation relative to the line-group axis; reflection parallel (h) or perpendicular (v).

The groups Cn(q) and Dn(q) express the symmetries of helical objects.

Nucleic acids have a well-defined direction, giving single strands C1(q).