\HeaderA{grid.null}{Null Graphical Object}{grid.null}
\aliasA{nullGrob}{grid.null}{nullGrob}
\keyword{dplot}{grid.null}
\begin{Description}\relax
These functions create a NULL graphical object,
which has zero width, zero height, and draw nothing.
It can be used as a place-holder or as an invisible
reference point for other drawing.
\end{Description}
\begin{Usage}
\begin{verbatim}
nullGrob(x = unit(0.5, "npc"), y = unit(0.5, "npc"),
         default.units = "npc",
         name = NULL, vp = NULL)
grid.null(...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] A numeric vector or unit object specifying x-location.
\item[\code{y}] A numeric vector or unit object specifying y-location.
\item[\code{default.units}] A string indicating the default units to use
if \code{x}, \code{y}, \code{width}, or \code{height}
are only given as numeric vectors.
\item[\code{name}] A character identifier. 
\item[\code{vp}] A Grid viewport object (or NULL).
\item[\code{...}] Arguments passed to \code{nullGrob()}.
\end{ldescription}
\end{Arguments}
\begin{Value}
A null grob.
\end{Value}
\begin{Author}\relax
Paul Murrell
\end{Author}
\begin{SeeAlso}\relax
\LinkA{Grid}{Grid},
\code{\LinkA{viewport}{viewport}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
grid.newpage()
grid.null(name="ref")
grid.rect(height=grobHeight("ref"))
grid.segments(0, 0, grobX("ref", 0), grobY("ref", 0))
\end{ExampleCode}
\end{Examples}

