spatstat (version 1.45-2)

as.ppp: Convert Data To Class ppp

Description

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

Usage

as.ppp(X, ..., fatal=TRUE)
  ## S3 method for class 'ppp':
as.ppp(X, \dots, fatal=TRUE)
  ## S3 method for class 'psp':
as.ppp(X, \dots, fatal=TRUE)
  ## S3 method for class 'quad':
as.ppp(X, \dots, fatal=TRUE)
  ## S3 method for class 'matrix':
as.ppp(X, W=NULL, \dots, fatal=TRUE)
  ## S3 method for class 'data.frame':
as.ppp(X, W=NULL, \dots, fatal=TRUE)
  ## S3 method for class 'influence.ppm':
as.ppp(X, \dots)
  ## S3 method for class 'default':
as.ppp(X, W=NULL, \dots, fatal=TRUE)

Arguments

X

Data which will be converted into a point pattern

W

Data which define a window for the pattern, when X does not contain a window. (Ignored if X contains window information.)

...

Ignored.

fatal

Logical value specifying what to do if the data cannot be converted. 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.

Details

Converts the dataset X to a point pattern (an object of class "ppp"; see ppp.object for an overview).

This function is normally used to convert an existing point pattern dataset, stored in another format, to the "ppp" format. To create a new point pattern from raw data such as $x,y$ coordinates, it is normally easier to use the creator function ppp.

The function as.ppp is generic, with methods for the classes "ppp", "psp", "quad", "matrix", "data.frame" and a default method.

The dataset X may be:

• an object of class"ppp"
• an object of class"psp"
• a point pattern object created by thespatiallibrary
• an object of class"quad"representing a quadrature scheme (seequad.object)
• a matrix or data frame with at least two columns
• a structure with entriesx,ywhich are numeric vectors of equal length
• a numeric vector of length 2, interpreted as the coordinates of a single point.

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

If X is a line segment pattern (an object of class psp) the point pattern returned consists of the endpoints of the segments. If X is marked then the point pattern returned will also be marked, the mark associated with a point being the mark of the segment of which that point was an endpoint.

If X is a matrix or data frame, the first and second columns will be interpreted as the $x$ and $y$ coordinates respectively. Any additional columns will be interpreted as marks. 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.

In the spatial library, a point pattern is represented in either of the following formats:

• (inspatialversions 1 to 6) a structure with entriesx,yxl,xu,yl,yu
• (inspatialversion 7) a structure with entriesx,yandarea, whereareais a structure with entriesxl,xu,yl,yu

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.

See Also

ppp, ppp.object, as.owin, owin.object

Examples

xy <- matrix(runif(40), ncol=2)
 pp <- as.ppp(xy, c(0,1,0,1))

 # Venables-Ripley format
 # check for 'spatial' package
 spatialpath <- system.file(package="spatial")
 if(nchar(spatialpath) > 0) {
   require(spatial)
   towns <- ppinit("towns.dat")
   pp <- as.ppp(towns) # converted to our format
   detach(package:spatial)
 }

 xyzt <- matrix(runif(40), ncol=4)
 Z <- as.ppp(xyzt, square(1))