grobX                  package:grid                  R Documentation

Create a Unit Describing a Grob Boundary Location

Description:

     These functions create a unit object describing a location
     somewhere on the boundary of a grob.  They are generic.

Usage:

     grobX(x, theta)
     grobY(x, theta)

Arguments:

       x: A grob, or gList, or gTree, or gPath.

   theta: An angle indicating where the location is on the grob
          boundary.  Can be one of '"east"', '"north"', '"west"', or
          '"south"', which correspond to angles 0, 90, 180, and 270,
          respectively.

Details:

     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, the boundary value will
     either correspond to the edge of a bounding box around all of the
     shapes described by the grob (for multiple rectangles, circles,
     xsplines, or text), or to a  convex hull around all vertices of
     all shapes described by the grob (for multiple polygons, points,
     lines, polylines,  and segments).

     Points grobs are currently a special case because the convex hull
     is based on the data symbol _locations_ and does not take into
     account the extent of the data symbols themselves.

     The extents of any arrow heads are currently _not_ taken into
     account.

Value:

     A unit object.

Author(s):

     Paul Murrell

See Also:

     'unit' and 'grobWidth'

