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The word "direction" in first instance indicates the degree of obliquity relative to the repeatunits which
represent the regular shiftpattern which in every case underlies a planesymmetry (wallpapergroup).
But dependent on the occurence of other element of symmetry (rotations, reflections, slide-reflections),
a "direction" besides a degree of obliquity can possess different orientations in space.
In those cases a direction is defined by its degree of obliquity and its orientation in space |
 | 6 orientations
in space |
|
 |
obliquity = 2/5
orientation = II
| |
 |
obliquity = 2/5
orientation = IV
|
| The values 2 and 5 on the coordinates, for each orentation of course can be reversed. As long as
there occur no reflections besides rotation in, the way the valyes are positioned needs to be consistent in
the sense that it must be in accordance with the rotationsymmetry in quesdtion. |