\HeaderA{Axis}{Generic function to add an Axis to a Plot}{Axis}
\keyword{aplot}{Axis}
\begin{Description}\relax
Generic function to add a suitable axis to the current plot.
\end{Description}
\begin{Usage}
\begin{verbatim}
Axis(x = NULL, at = NULL, ..., side, labels = NULL)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] an object which indicates the range over which an axis should
be drawn
\item[\code{at}] the points at which tick-marks are to be drawn.
\item[\code{side}] an integer specifying which side of the plot the axis is
to be drawn on.  The axis is placed as follows: 1=below,
2=left, 3=above and 4=right.
\item[\code{labels}] this can either be a logical value specifying whether
(numerical) annotations are to be made at the tickmarks, or a
character or expression vector of labels to be placed at the
tickpoints. If this is specified as a character or expression
vector, \code{at} should be supplied and they should be the same
length.
\item[\code{...}] Arguments to be passed to methods and perhaps then to
\code{\LinkA{axis}{axis}}.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
This is a generic function.  It works in a slightly non-standard way:
if \code{x} is supplied and non-NULL it dispatches on \code{x},
otherwise if \code{at} is supplied and non-NULL it dispatches on \code{at},
and the default action is to call \code{\LinkA{axis}{axis}}, omitting argument
\code{x}.

The idea is that for plots for which either or both of the axes are
numerical but with a special interpretation, the standard plotting
functions (including \code{\LinkA{boxplot}{boxplot}}, \code{\LinkA{contour}{contour}},
\code{\LinkA{coplot}{coplot}}, \code{\LinkA{filled.contour}{filled.contour}},
\code{\LinkA{pairs}{pairs}}, \code{\LinkA{plot.default}{plot.default}}, \code{\LinkA{rug}{rug}} and
\code{\LinkA{stripchart}{stripchart}}) will set up user coordinates and \code{Axis}
will be called to label them appropriately.

There are \code{"Date"}, \code{"POSIXct"} and \code{"POSIXlt"}
methods which can pass an argument \code{format} onto the
appropriate \code{axis} method (see \code{\LinkA{axis.POSIXct}{axis.POSIXct}}).
\end{Details}
\begin{Value}
The numeric locations on the axis scale at which tick marks were drawn
when the plot was first drawn (see \sQuote{Details}).

This function is usually invoked for its side effect, which is to add
an axis to an already existing plot.
\end{Value}
\begin{SeeAlso}\relax
\code{\LinkA{axis}{axis}}.
\end{SeeAlso}

