polyConstruct {RSurvey} | R Documentation

## Polygon Construction

### Description

Read polygon information from a text file.

### Usage

    polyConstruct(file = NULL, dl = NULL)

### Arguments

`file` | either a character string naming a file or a connection.
`dl` | the maximum distance between polygon vertices. If `NULL`, no vertices are added.

### Format

The tab delineated text file, ‘*.txt’, adheres to the following 4 column format:

`[,1]` | integer | an index for vertices within a polygon.
`[,2]` | numeric | vertex location in the x-direction.
`[,3]` | numeric | vertex location in the y-direction.
`[,4]` | integer | a code, see Details.

### Details

The `code` argument is used to identify polygons and vertex types. Letting `code = 0` for two sequential vertices will override `dl` and prevent additional vertices from being added between them. A `code < 2` indicates a vertex point is within the outer polygon. Inner polygons or holes are specified with a `code > 1`.

### Value

A polygon of class `gpc.poly-class`.

### Author(s)

Fisher, J. C.

### See Also

`polyfile`

### Examples

    f <- system.file("RSurvey-ex/confluence-poly.txt", package = "RSurvey")
    con <- file(f, open = "r", encoding = "latin1")
    ply <- polyConstruct(file = con)
    pts <- get.pts(ply)
    plot(ply)
    for(i in 1:length(pts)) points(get.pts(ply)[[i]], col = "red")

    con <- file(f, open = "r", encoding = "latin1")
    ply <- polyConstruct(file = con, dl = 1)
    pts <- get.pts(ply)
    for(i in 1:length(pts)) points(get.pts(ply)[[i]], col = "green")

[Package RSurvey version 0.4.5 Index]