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

 new-generics R Documentation

## Generics/Methods for polygon objects

### Description

Some generic functions and methods for polygon objects

### Usage

``````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.

### Examples

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

rgeos documentation built on July 26, 2023, 5:42 p.m.