
Most of the surfaces studied by the Scientific Graphics Project and all those illustrated in these pages have one or more symmetries. Symmetries are attributed to an object based on its ability to remain invarient under certain rigid transformations. Such transformations are called symmetry operations for that object. Symmetry operations in R3 belong to one of the following types, where the italicized geometric objects specify the symmetry.
In addition, the operation rotoinversion, or improper rotation, is sometimes included in this list. However, it can be constituted as a rotation followed by an inversion.
Applied to continuous surfaces, there are two types of rotation axes: twofold axes lying on the surface, and nfold axes which intersect the surface perpendicularly if they intersect the surface. This is reflected in the notation described below.
Notation used here
Where the symmetries are described for surfaces in the SGP web, the following notation is used:
Symmetry Groups
As an alternative to describing all of the symmetry operations for each surface, one could also assign most of them to previously described symmetry groups. This would be particularly useful in the case of triply periodic surfaces since the symmetry operations tend to be numerous but each must belong to one of the possible 230 space (symmetry) groups.