Plot a Variogram, Covariogram or Correlogram
DESCRIPTION:
Display a variogram, covariogram or correlogram object. A multipanel display is created if there is more than one level in the azimuth factor in x.
USAGE: 
plot.variogram(x, panel=panel.xyplot, ...)
plot.covariogram(x, panel=panel.xyplot, ...)
plot.correlogram(x, panel=panel.xyplot, ...)
REQUIRED ARGUMENTS:
x:
for plot.variogram, an object of class "variogram", usually created by the function variogram. For plot.covariogram, an object of class "covariogram", usually created by the function covariogram. For plot.correlogram, an object of class "correlogram", usually created by the function correlogram.
OPTIONAL ARGUMENTS:
panel:
a function of two arguments, x and y, that draws the data display in each panel. The default, panel.xyplot, draws points (or lines if type="l" is also an argument in the function call).

Graphical parameters may also be supplied as arguments to this function (see par). If a multipanel display is to be drawn then the possible graphical parameters are described in the trellis.args help file.

SIDE EFFECTS:
a plot is produced on the current graphics device.
DETAILS:
These functions are methods for the generic function plot for objects of classes "variogram", "covariogram" and "correlogram". They can be invoked by calling plot for an object of the appropriate class.

The axes on the graph are set to include the point (0,0) for all plots by default. The function plot.correlogram sets the y axis limits to (-1,1).

If the azimuth component of x has only one level then a standard plot is made of the covariance measure (variogram, covariance or correlation) versus x$distance. The function panel is still used to draw the points on this standard plot. If there is more than one level in the azimuth component then a multipanel display is drawn using the Trellis function xyplot. Each panel contains a plot of the covariance measure versus x$distance for a particular level of x$azimuth.

The default panel function, panel.xyplot, uses the trellis.settings list for setting pch, col, cex when plotting the points. As such, the plots are best displayed on a device started with the function trellis.device.

SEE ALSO:
correlogram , covariogram , panel.xyplot , plot , trellis.args, trellis.device , trellis.settings , variogram .
EXAMPLES: 
trellis.device()     # start the default trellis graphics device
vg1 <- variogram(log(tcatch+1) ~ long + lat, data=scallops)
plot(vg1)     # a single panel display
vg4 <- variogram(log(tcatch+1) ~ long + lat, data=scallops,
        azimuth=c(0,45,90,135), tol.azimuth=22.5)
plot(vg4, panel=function(x,y,...) {
        panel.xyplot(x,y,...)
        panel.loess(x,y,...) })     # a 4 panel display with loess smooths