
grid.curve  Draw a Curve Between Locations  Description These functions create and draw a curve from one location to another.  Usage 
grid.curve(...)
curveGrob(x1, y1, x2, y2, default.units = "npc",
          curvature = 1, angle = 90, ncp = 1, shape = 0.5,
          square = TRUE, squareShape = 1,
          inflect = FALSE, arrow = NULL, open = TRUE,
          debug = FALSE,
          name = NULL, gp = gpar(), vp = NULL)
arcCurvature(theta)
 Arguments  
x1  A numeric vector or unit object specifying the x-location of the start point. 
 
y1  A numeric vector or unit object specifying the y-location of the start point. 
 
x2  A numeric vector or unit object specifying the x-location of the end point. 
 
y2  A numeric vector or unit object specifying the y-location of the end point. 
 
default.units  A string indicating the default units to use if x1, y1, x2 or y2 are only given as numeric values. 
 
curvature  A numeric value giving the amount of curvature. Negative values produce left-hand curves, positive values produce right-hand curves, and zero produces a straight line. 
 
angle  A numeric value between 0 and 180, giving an amount to skew the control points of the curve. Values less than 90 skew the curve towards the start point and values greater than 90 skew the curve towards the end point. 
 
ncp  The number of control points used to draw the curve. More control points creates a smoother curve. 
 
shape  A numeric vector of values between -1 and 1, which control the shape of the curve relative to its control points. See grid.xspline for more details. 
 
square  A logical value that controls whether control points for the curve are created city-block fashion or obliquely. When ncp is 1 and angle is 90, this is typically TRUE, otherwise this should probably be set to FALSE (see Examples below). 
 
squareShape  A shape value to control the behaviour of the curve relative to any additional control point that is inserted if square is TRUE. 
 
inflect  A logical value specifying whether the curve should be cut in half and inverted (see Examples below). 
 
arrow  A list describing arrow heads to place at either end of the curve, as produced by the arrow function. 
 
open  A logical value indicating whether to close the curve (connect the start and end points). 
 
debug  A logical value indicating whether debugging information should be drawn. 
 
name   A character identifier.  
 
gp  An object of class "gpar", typically the output from a call to the function gpar. This is basically a list of graphical parameter settings. 
 
vp  A Grid viewport object (or NULL). 
 
...  Arguments to be passed to curveGrob. 
 
theta  An angle (in degrees). 
  Details Both functions create a curve grob (a graphical object describing an curve), but only grid.curve draws the curve.  The arcCurvature function can be used to calculate a curvature such that control points are generated on an arc corresponding to angle theta. This is typically used in conjunction with a large ncp to produce a curve corresponding to the desired arc.  Value A grob object.  See Also Grid, viewport, grid.xspline, arrow  Examples 
curveTest <- function(i, j, ...) {
  pushViewport(viewport(layout.pos.col=j, layout.pos.row=i))
  do.call("grid.curve", c(list(x1=.25, y1=.25, x2=.75, y2=.75), list(...)))
  grid.text(sub("list\\((.*)\\)", "\\1",
                deparse(substitute(list(...)))),
            y=unit(1, "npc"))
  popViewport()
}
# grid.newpage()
pushViewport(plotViewport(c(0, 0, 1, 0),
                          layout=grid.layout(2, 1, heights=c(2, 1))))
pushViewport(viewport(layout.pos.row=1,
                      layout=grid.layout(3, 3, respect=TRUE)))
curveTest(1, 1)
curveTest(1, 2, inflect=TRUE)
curveTest(1, 3, angle=135)
curveTest(2, 1, arrow=arrow())
curveTest(2, 2, ncp=8)
curveTest(2, 3, shape=0)
curveTest(3, 1, curvature=-1)
curveTest(3, 2, square=FALSE)
curveTest(3, 3, debug=TRUE)
popViewport()
pushViewport(viewport(layout.pos.row=2,
                      layout=grid.layout(3, 3)))
curveTest(1, 1)
curveTest(1, 2, inflect=TRUE)
curveTest(1, 3, angle=135)
curveTest(2, 1, arrow=arrow())
curveTest(2, 2, ncp=8)
curveTest(2, 3, shape=0)
curveTest(3, 1, curvature=-1)
curveTest(3, 2, square=FALSE)
curveTest(3, 3, debug=TRUE)
popViewport(2)


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