# gpc-new-generics: Generics/Methods for polygon objects In rgeos: Interface to Geometry Engine - Open Source ('GEOS')

## Description

Some generic functions and methods for polygon objects

## Usage

 ```1 2 3 4 5 6 7``` ```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

## 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.

## 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.

## Author(s)

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

`"gpc.poly"` class documentation.
 ```1 2 3 4``` ```holepoly <- read.polyfile(system.file("poly-ex-gpc/hole-poly.txt", package ="rgeos"), nohole = FALSE) area.poly(holepoly) stopifnot(area.poly(holepoly) == 8) ```