infline {spatstat.geom}

Infinite Straight Lines

Description

Define the coordinates of one or more straight lines in the plane

Usage

infline(a = NULL, b = NULL, h = NULL, v = NULL, p = NULL, theta = NULL)

## S3 method for class 'infline'
print(x, ...)

## S3 method for class 'infline'
plot(x, ...)

Arguments

a, b

Numeric vectors of equal length giving the intercepts a and slopes b of the lines. Incompatible with h,v,p,theta

h

Numeric vector giving the positions of horizontal lines when they cross the y axis. Incompatible with a,b,v,p,theta

v

Numeric vector giving the positions of vertical lines when they cross the x axis. Incompatible with a,b,h,p,theta

p, theta

Numeric vectors of equal length giving the polar coordinates of the line. Incompatible with a,b,h,v

x

An object of class "infline"

...

Extra arguments passed to print for printing or abline for plotting

Details

The class infline is a convenient way to handle infinite straight lines in the plane.

The position of a line can be specified in several ways:

• its intercept a and slope b in the equation y = a + b x can be used unless the line is vertical.

• for vertical lines we can use the position v where the line crosses the y axis

• for horizontal lines we can use the position h where the line crosses the x axis

• the polar coordinates p and \theta can be used for any line. The line equation is

  x \cos\theta + y \sin\theta = p

The command infline will accept line coordinates in any of these formats. The arguments a,b,h,v have the same interpretation as they do in the line-plotting function abline.

The command infline converts between different coordinate systems (e.g. from a,b to p,theta) and returns an object of class "infline" that contains a representation of the lines in each appropriate coordinate system. This object can be printed and plotted.

Value

The value of infline is an object of class "infline" which is basically a data frame with columns a,b,h,v,p,theta. Each row of the data frame represents one line. Entries may be NA if a coordinate is not applicable to a particular line.

Author(s)

Adrian Baddeley [e-mail] and Rolf Turner [e-mail].

See Also

rotate.infline, clip.infline, chop.tess, whichhalfplane

Examples

  infline(a=10:13,b=1)
  infline(p=1:3, theta=pi/4)
  plot(c(-1,1),c(-1,1),type="n",xlab="",ylab="", asp=1)
  plot(infline(p=0.4, theta=seq(0,pi,length=20)))