as.ppp: Convert Data To Class ppp

Description

Tries to coerce any reasonable kind of data to a point pattern (an object of class "ppp") for use by the spatstat package).

Usage

as.ppp(X)
  as.ppp(X, W)
  as.ppp(X, fatal=TRUE)

Arguments

Data which will be converted into a point pattern

Data which define a default window for the pattern

fatal

Logical value. See Details.

Value

An object of class "ppp" (see ppp.object) describing the point pattern and its window of observation. The value NULL may also be returned; see Details.

synopsis

as.ppp(X, W=NULL, fatal=TRUE)

Warnings

If the format of spp objects is changed in future versions of the spatial library, then as.ppp may not be able to interpret them. It currently handles all versions of spatial up to 7.1-4.

Details

This function tries to coerce the data X to a point pattern (an object of class "ppp"; see ppp.object for an overview). The optional argument W is a default window for the pattern; it is used only if a window is not specified in X.

The data X may be:

an object of class"ppp"
an object of class"spp"as defined in thespatiallibrary
an object of class"quad"representing a quadrature scheme (seequad.object)
a two-column matrix
a structure with entriesx,y

In the last two cases, we need the second argument W which is converted to a window object by the function as.owin. In the first three cases, W will be ignored.

The argument fatal indicates what to do when W is missing and X contains no information about the window. If fatal=TRUE, a fatal error will be generated; if fatal=FALSE, the value NULL is returned.

An spp object is the representation of a point pattern in the spatial library. Our implementation recognises the following formats:

a structure with entriesx,yxl,xu,yl,yu
a structure with entriesx,yandarea, whereareais a structure with entriesxl,xu,yl,yu

(used in spatial versions 1 to 6 and version 7.1 respectively) where x and y are vectors of equal length giving the point coordinates, and xl, xu, yl, yu are numbers giving the dimensions of a rectangular window.

Point pattern datasets can also be created by the function ppp.

Examples

Run this code

library(spatstat)

 plot(c(0,1),c(0,1),type="n")
 xy <- locator(20) # click on 20 points in plot window
 pp <- as.ppp(xy, c(0,1,0,1))
 
 w <- owin(c(0,1),c(0,1))
 plot(w)                      # neater
 xy <- locator(20)            # click on 20 points in plot window
 pp <- as.ppp(xy, w) 
 
 xy <- matrix(runif(40), ncol=2)
 pp <- as.ppp(xy, c(0,1,0,1))
 
 # Venables-Ripley format
 sp <- list(x=runif(10), y=runif(10), xl=0, xu=1, yl=0, yu=1)
 pp <- as.ppp(sp)   # converted to our format

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