spatstat (version 1.23-1)

superimpose: Superimpose Several Geometric Patterns

Description

Superimpose any number of point patterns or line segment patterns.

Usage

superimpose(...)
  ## S3 method for class 'ppp':
superimpose(\dots, W=NULL, check=TRUE)
  ## S3 method for class 'psp':
superimpose(\dots, W=NULL, check=TRUE)
  ## S3 method for class 'default':
superimpose(\dots, W=NULL, check=TRUE)

Arguments

...

Any number of arguments, each of which represents either a point pattern or a line segment pattern.

W

Optional. Data determining the window for the resulting pattern. Either a window (object of class "owin", or something acceptable to as.owin), or a function which returns a window,

check

Logical value (passed to ppp or psp as appropriate) determining whether to check the geometrical validity of the resulting pattern.

Value

• For superimpose.ppp, a point pattern (object of class "ppp"). For superimpose.default, either a point pattern (object of class "ppp") or a list(x,y). For superimpose.psp, a line segment pattern (object of class "psp").

Details

This function is used to superimpose several geometric patterns of the same kind, producing a single pattern of the same kind. The function superimpose is generic, with methods for the class ppp of point patterns, the class psp of line segment patterns, and a default method. The dispatch to a method is determined by the class of the first argument in ....

• default: If the first argument isnotan object of classppporpsp, then the default methodsuperimpose.defaultis executed. All arguments in...must have componentsxandyrepresenting spatial coordinates. They may include objects of classppp. The result will be either alist(x,y)or a point pattern (objects of classppp) as explained below.
• ppp: If the first...argument is an object of classpppthen the methodsuperimpose.pppis executed. All arguments in...must be eitherpppobjects or lists with componentsxandy. The result will be an object of classppp.
• psp: If the first...argument is an object of classpspthen thepspmethod is dispatched and all...arguments must bepspobjects. The result is apspobject.

The patterns are not required to have the same window of observation.

The window for the superimposed pattern is controlled by the argument W.

• IfWis a window (object of class"W"or something acceptable toas.owin) then this determines the window for the superimposed pattern.
• IfWisNULL, or the character string"none", then windows are extracted from the geometric patterns, as follows. Forsuperimpose.psp, all arguments...are line segment patterns (objects of class"psp"); their observation windows are extracted; the union of these windows is computed; and this union is taken to be the window for the superimposed pattern. Forsuperimpose.pppandsuperimpose.default, the arguments...are inspected, and any arguments which are point patterns (objects of class"ppp") are selected; their observation windows are extracted, and the union of these windows is taken to be the window for the superimposed point pattern. Forsuperimpose.defaultif none of the arguments is of class"ppp"then no window is computed and the result ofsuperimposeis alist(x,y).
• IfWis one of the strings"convex","rectangle"or"bbox"then a window for the superimposed pattern is computed from the coordinates of the points or the line segments as follows.[object Object],[object Object],[object Object]
• IfWis a function, then this function is used to compute a window for the superimposed pattern from the coordinates of the points or the line segments. The function should accept input of the formlist(x,y)and is expected to return an object of class"owin". Examples of such functions areriprasandbounding.box.xy.

The arguments ... may be marked patterns. The marks of each component pattern must have the same format. Numeric and character marks may be ``mixed''. If there is such mixing then the numeric marks are coerced to character in the combining process. If the mark structures are all data frames, then these data frames must have the same number of columns and identical column names.

If the arguments ... are given in the form name=value, then the names will be used as an extra column of marks attached to the elements of the corresponding patterns.

See Also

concatxy, quadscheme.

Examples

# superimposing point patterns
  p1  <- runifrect(30)
  p2  <- runifrect(42)
  s1  <- superimpose(p1,p2) # Unmarked pattern.
  p3  <- list(x=rnorm(20),y=rnorm(20))
  s2  <- superimpose(p3,p2,p1) # Default method gets called.
  s2a <- superimpose(p1,p2,p3) # Same as s2 except for order of points.
  s3  <- superimpose(clyde=p1,irving=p2) # Marked pattern; marks a factor
                                         # with levels "clyde" and "irving";
                                         # warning given.
  marks(p1) <- factor(sample(LETTERS[1:3],30,TRUE))
  marks(p2) <- factor(sample(LETTERS[1:3],42,TRUE))
  s5  <- superimpose(clyde=p1,irving=p2) # Marked pattern with extra column
  marks(p2) <- data.frame(a=marks(p2),b=runif(42))
  s6  <- try(superimpose(p1,p2)) # Gives an error.
  marks(p1) <- data.frame(a=marks(p1),b=1:30)
  s7  <- superimpose(p1,p2) # O.K.

  # how to make a 2-type point pattern with types "a" and "b"
  u <- superimpose(a = rpoispp(10), b = rpoispp(20))

  # how to make a 2-type point pattern with types 1 and 2
  u <- superimpose("1" = rpoispp(10), "2" = rpoispp(20))
 
  # superimposing line segment patterns
  X <- rpoisline(10)
  Y <- as.psp(matrix(runif(40), 10, 4), window=owin())
  Z <- superimpose(X, Y)

  # being unreasonable
  crud <- superimpose(p1,p2,X,Y) # Gives an error, of course!