This class is used to represent coordinate systems. It does this
in rather the same way that a frame around a graph describes the
coordinate space in which data are plotted. Consequently, a
Frame has a TitleTitle (string) attribute, which describes the
coordinate space, and contains axes which in turn hold
information such as Label and Units strings which are used for
labelling (e.g.) graphical output. In general, however, the
number of axes is not restricted to two.
Functions are available for converting Frame coordinate values
into a form suitable for display, and also for calculating
distances and offsets between positions within the Frame.
Frames may also contain knowledge of how to transform to and
from related coordinate systems.