\HeaderA{grobX}{Create a Unit Describing a Grob Boundary Location}{grobX}
\aliasA{grobY}{grobX}{grobY}
\keyword{dplot}{grobX}
\begin{Description}\relax
These functions create a unit object describing a location somewhere
on the boundary of
a grob.  They are generic.
\end{Description}
\begin{Usage}
\begin{verbatim}
grobX(x, theta)
grobY(x, theta)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] A grob, or gList, or gTree, or gPath.
\item[\code{theta}] An angle indicating where the location is
on the grob boundary.  Can be one of \code{"east"},
\code{"north"}, \code{"west"}, or \code{"south"},
which correspond to angles 0, 90, 180, and 270,
respectively.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The angle is anti-clockwise with zero corresponding to a line
with an origin centred between the extreme
points of the shape, and pointing at 3 o'clock.

If the grob describes a single shape, the boundary value should
correspond to the exact edge of the shape.

If the grob describes multiple shapes, in most cases, the boundary
value will correspond to the edge of a bounding box around all of
the shapes.  The exception to this is a polygon grob describing
multiple polygons;  in that case, the edge corresponds to a
convex hull around all points of all polygons described by the grob.
\end{Details}
\begin{Value}
A unit object.
\end{Value}
\begin{Author}\relax
Paul Murrell
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{unit}{unit}} and
\code{\LinkA{grobWidth}{grobWidth}}
\end{SeeAlso}

