Some generic functions and methods for polygon objects

```
append.poly(x, y)
area.poly(object, ...)
get.pts(object)
get.bbox(x)
scale.poly(x, ...)
tristrip(x)
triangulate(x)
```

## Arguments

- x,object
A polygon object

- y
A polygon object

- ...
Other arguments passed to methods

## Methods

- append.poly
```
signature(x = "gpc.poly", y =
"gpc.poly")
```

: Combine all contours of two `"gpc.poly"`

objects and return the combined polygon as a `"gpc.poly"`

object.

- area.poly
`signature(object = "gpc.poly")`

: Compute and
return the sum of the areas of all contours in a `"gpc.poly"`

object.

- scale.poly
`signature(x = "gpc.poly")`

: Scale (divide)
the x and y coordinates of a `"gpc.poly"`

object by the
amount `xscale`

and `yscale`

, respectively. Return a
scaled `"gpc.poly"`

object.

- get.pts
`signature(object = "gpc.poly")`

: Return the
list of x and y coordinates of the vertices of a `"gpc.poly"`

object.

- get.bbox
`signature(x = "gpc.poly")`

: Return the
bounding box for a `"gpc.poly"`

object.

- tristrip
`signature(x = "gpc.poly")`

: Return a tristrip
list for a `"gpc.poly"`

object.

- triangulate
`signature(x = "gpc.poly")`

: Return a matrix
of vertices of a triangulation of a `"gpc.poly"`

object.

## Details

The result of `tristrip(x)`

is a list of two-column matrices. Each
matrix is a tristrip, i.e. the rows are vertices of triangles, with
each overlapping triple of rows corresponding to a separate triangle.

The result of `triangulate(x)`

is a single two-column matrix. The
rows are vertices of triangles, taken in non-overlapping triples.

## Author

Roger D. Peng; GPC Library by Alan Murta; tristrip additions by
Duncan Murdoch

## See also

`"gpc.poly"`

class documentation.

## Examples

```
holepoly <- read.polyfile(system.file("poly-ex-gpc/hole-poly.txt",
package ="rgeos"), nohole = FALSE)
area.poly(holepoly)
#> [1] 8
stopifnot(area.poly(holepoly) == 8)
```