spatstat (version 1.23-1)

as.psp: 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, \dots, check=FALSE, fatal=TRUE)
  ## S3 method for class 'data.frame':
as.psp(x, \dots, window=NULL, marks=NULL, check=spatstat.options("checksegments"), fatal=TRUE)
  ## S3 method for class 'matrix':
as.psp(x, \dots, window=NULL, marks=NULL, check=spatstat.options("checksegments"),
fatal=TRUE)
  ## S3 method for class 'owin':
as.psp(x, \dots, check=spatstat.options("checksegments"), fatal=TRUE)
  ## S3 method for class 'default':
as.psp(x, \dots, 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 when x does not contain a window

...

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.

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.

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 namedx0, y0, x1, y1or elements namedxmid, ymid, length, angleand possibly a fifth element namedmarks
• an object of class"owin"representing a spatial window; it must be of type"rectangle"or"polygonal". The boundary edges of the window will be extracted as a line segment pattern.

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

• If there are columns namedx0, y0, x1, y1then these will be interpreted as the coordinates of the endpoints of the segments and used to form theendscomponent of thepspobject to be returned.
• If there are columns namedxmid, ymid, length, anglethen 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 theendscomponent of thepspobject to be returned.
• If there is a column namedmarksthen this will be interpreted as the marks of the pattern provided that the argumentmarksof this function isNULL. If argumentmarksis notNULLthen the value of this argument is taken to be the marks of the pattern and the column namedmarksis ignored (with a warning). In either case the column named marks is deleted and omitted from further consideration.
• If there is no column namedmarksand if themarksargument of this function isNULL, and if after interpreting 4 columns ofxas determining theendscomponent of thepspobject to be returned, there remain other columns ofx, then these remaining columns will be taken to form a data frame of marks for thepspobject 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.

See Also

psp, psp.object, as.owin, owin.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=runifpoint(10), to=runifpoint(10))