plot a Spatial Point Pattern

Description

Plot a two-dimensional spatial point pattern

Usage

 ## S3 method for class 'ppp':
 plot(x, main, ..., chars, cols, use.marks=TRUE, add=FALSE,
maxsize, markscale)

Arguments

Details

This is the plot method for point pattern datasets (of class "ppp", see ppp.object).

First the observation window x$window is plotted. Then the points themselves are plotted, in a fashion that depends on their marks, as follows.

unmarked point pattern:

If the point pattern does not have marks, or if use.marks = FALSE, then the locations of all points will be plotted using a single plot character

multitype point pattern:

If x$marks is a factor, then each level of the factor is represented by a different plot character.

continuous marks:

If x$marks is a numeric vector, the marks are rescaled to the unit interval and each point is represented by a circle with radius proportional to the rescaled mark (if the value is positive) or a square with side proportional to the absolute value of the rescaled mark (if the value is negative).

other kinds of marks:

If x$marks is neither numeric nor a factor, then each possible mark will be represented by a different plotting character. The default is to represent the ith smallest mark value by points(..., pch=i).

Plotting of the window x$window is performed by plot.owin. This plot may be modified through the ... arguments. In particular the extra argument border determines the colour of the window.

Plotting of the points themselves is performed by the function points, except for the case of continuous marks, where it is performed by symbols. Their plotting behaviour may be modified through the ... arguments.

The argument chars determines the plotting character or characters used to display the points (in all cases except for the case of continuous marks). For an unmarked point pattern, this should be a single integer or character determining a plotting character (see par("pch")). For a multitype point pattern, chars should be a vector of integers or characters, of the same length as levels(x$marks), and then the ith level or type will be plotted using character chars[i].

If chars is absent, but there is an extra argument pch, then this will determine the plotting character for all points.

The argument cols determines the colour or colours used to display the points. For an unmarked point pattern, or a marked point pattern with continuous marks, this should be a character string determining a colour. For a multitype point pattern, cols should be a character vector, of the same length as levels(x$marks). The ith level or type will be plotted using colour cols[i].

If cols is absent, the colour used to plot all the points may be determined by the extra argument fg (for multitype point patterns) or the extra argument col (for all other cases). Note that col will also reset the colour of the window.

The arguments maxsize and markscale incompatible. They control the physical size of the circles and squares which represent the marks in a point pattern with continuous marks. If markscale is given, then a mark value of m is plotted as a circle of radius m * markscale (if m is positive) or a square of side abs(m) * markscale (if m is negative). If maxsize is given, then the largest mark in absolute value, mmax=max(abs(x$marks)), will be scaled to have physical size maxsize.

The user can set the default values of these plotting parameters using spatstat.options("par.points").

The value returned by this plot function can be used to make a suitable legend, as shown in the examples.

Value

NULL, or a vector giving the correspondence between mark values and plotting characters.

Author(s)

Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner rolf@math.unb.ca http://www.math.unb.ca/~rolf

See Also

ppp.object, plot, par, points, plot.owin, symbols

Examples

   data(cells)
   plot(cells)

   plot(cells, pch=16)

   # make the plotting symbols larger (for publication at reduced scale)
   plot(cells, cex=2)

   # set it in spatstat.options
   oldopt <- spatstat.options(par.points=list(cex=2))
   plot(cells)
   spatstat.options(oldopt)

   # multitype 
   data(lansing)
   plot(lansing)

   # marked by a real number
   data(longleaf)
   plot(longleaf)

   # just plot the points
   plot(longleaf, use.marks=FALSE)
   plot(unmark(longleaf)) # equivalent

   # controlling COLOURS of points
   plot(cells, cols="blue")
   plot(lansing, cols=c("black", "yellow", "green", 
                        "blue","red","pink"))
   plot(longleaf, fg="blue")

   # make window purple
   plot(lansing, border="purple")
   # make everything purple
   plot(lansing, border="purple", cols="purple", col.main="purple")
 
   # controlling PLOT CHARACTERS
   plot(lansing, chars = 11:16)
   plot(lansing, chars = c("o","h","m",".","o","o"))

   # controlling MARK SCALE
   plot(longleaf, markscale=0.1)

   # draw circles of DIAMETER equal to nearest neighbour distance
   plot(cells %mark% nndist(cells), markscale=1/2)

   # making the legend
   data(amacrine)
   v <- plot(amacrine)
   legend(0.2, 1.2, pch=v, legend=names(v))