# infline

From spatstat v1.18-2
by Adrian Baddeley

##### Infinite Straight Lines

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, \dots)
## S3 method for class 'infline':
plot(x, \dots)
```

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

`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.

##### 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)))
```

*Documentation reproduced from package spatstat, version 1.18-2, License: GPL (>= 2)*

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