R: Convert Data To Class ppp

as.ppp {spatstat.geom} | R Documentation

## 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, ..., fatal=TRUE)

      ## S3 method for class 'psp'
    as.ppp(X, ..., fatal=TRUE)

      ## S3 method for class 'quad'
    as.ppp(X, ..., fatal=TRUE)

      ## S3 method for class 'matrix'
    as.ppp(X, W=NULL, ..., fatal=TRUE)

      ## S3 method for class 'data.frame'
    as.ppp(X, W=NULL, ..., fatal=TRUE)

      ## Default S3 method:
    as.ppp(X, W=NULL, ..., 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.

### 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 the spatial library

- an object of class `"quad"` representing a quadrature scheme (see `quad.object`)

- a matrix or data frame with at least two columns

- a structure with entries `x`, `y` which 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:

- (in spatial versions 1 to 6) a structure with entries `x`, `y` `xl`, `xu`, `yl`, `yu`

- (in spatial version 7) a structure with entries `x`, `y` and `area`, where `area` is a structure with entries `xl`, `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`.

Methods for `as.ppp` exist for some other classes of data; they are listed by `methods(as.ppp)`.

### 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.

### Author(s)

Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk

### See Also

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

Methods for `as.ppp` exist for some other classes of data; they are listed by `methods(as.ppp)`.

### 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))

[Package spatstat.geom version 2.3-2 Index]