as.psp {spatstat.geom}

Convert Data To Class psp

Description

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

Usage

  as.psp(x, ..., from=NULL, to=NULL)

  ## S3 method for class 'psp'
as.psp(x, ..., check=FALSE, fatal=TRUE)

  ## S3 method for class 'data.frame'
as.psp(x, ..., window=NULL, marks=NULL,
      check=spatstat.options("checksegments"), fatal=TRUE)

  ## S3 method for class 'matrix'
as.psp(x, ..., window=NULL, marks=NULL,
       check=spatstat.options("checksegments"), fatal=TRUE)

  ## Default S3 method:
as.psp(x, ..., window=NULL, marks=NULL,
       check=spatstat.options("checksegments"), fatal=TRUE)

Arguments

x

Data which will be converted into a line segment pattern

window

Data which define a window for the pattern.

...

Ignored.

marks

(Optional) vector or data frame of marks for the pattern

check

Logical value indicating whether to check the validity of the data, e.g. to check that the line segments lie inside the window.

fatal

Logical value. See Details.

from, to

Point patterns (object of class "ppp") containing the first and second endpoints (respectively) of each segment. Incompatible with x.

Details

Converts the dataset x to a line segment pattern (an object of class "psp"; see psp.object for an overview).

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

The dataset x may be:

• an object of class "psp"

• a data frame with at least 4 columns

• a structure (list) with elements named x0, y0, x1, y1 or elements named xmid, ymid, length, angle and possibly a fifth element named marks

If x is a data frame the interpretation of its columns is as follows:

• If there are columns named x0, y0, x1, y1 then these will be interpreted as the coordinates of the endpoints of the segments and used to form the ends component of the psp object to be returned.

• If there are columns named xmid, ymid, length, angle then these will be interpreted as the coordinates of the segment midpoints, the lengths of the segments, and the orientations of the segments in radians and used to form the ends component of the psp object to be returned.

• If there is a column named marks then this will be interpreted as the marks of the pattern provided that the argument marks of this function is NULL. If argument marks is not NULL then the value of this argument is taken to be the marks of the pattern and the column named marks is ignored (with a warning). In either case the column named marks is deleted and omitted from further consideration.

• If there is no column named marks and if the marks argument of this function is NULL, and if after interpreting 4 columns of x as determining the ends component of the psp object to be returned, there remain other columns of x, then these remaining columns will be taken to form a data frame of marks for the psp object to be returned.

If x is a structure (list) with elements named x0, y0, x1, y1, marks or xmid, ymid, length, angle, marks, then the element named marks will be interpreted as the marks of the pattern provide that the argument marks of this function is NULL. If this argument is non-NULL then it is interpreted as the marks of the pattern and the element marks of x is ignored — with a warning.

Alternatively, you may specify two point patterns from and to containing the first and second endpoints of the line segments.

The argument window is converted to a window object by the function as.owin.

The argument fatal indicates what to do when the data cannot be converted to a line segment pattern. If fatal=TRUE, a fatal error will be generated; if fatal=FALSE, the value NULL is returned.

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

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

Value

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

Warnings

If only a proper subset of the names x0,y0,x1,y1 or xmid,ymid,length,angle appear amongst the names of the columns of x where x is a data frame, then these special names are ignored.

For example if the names of the columns were xmid,ymid,length,degrees, then these columns would be interpreted as if the represented x0,y0,x1,y1 in that order.

Whether it gets used or not, column named marks is always removed from x before any attempt to form the ends component of the psp object that is returned.

Author(s)

Adrian Baddeley [e-mail], Rolf Turner [e-mail] and Ege Rubak [e-mail].

See Also

psp, psp.object, as.owin, owin.object.

See edges for extracting the edges of a polygonal window as a "psp" object.

Examples

   mat <- matrix(runif(40), ncol=4)
   mx <- data.frame(v1=sample(1:4,10,TRUE),
                    v2=factor(sample(letters[1:4],10,TRUE),levels=letters[1:4]))
   a <- as.psp(mat, window=owin(),marks=mx)
   mat <- cbind(as.data.frame(mat),mx)
   b <- as.psp(mat, window=owin()) # a and b are identical.
   stuff <- list(xmid=runif(10),
                 ymid=runif(10),
                 length=rep(0.1, 10),
                 angle=runif(10, 0, 2 * pi))
   a <- as.psp(stuff, window=owin())
   b <- as.psp(from=runifrect(10), to=runifrect(10))