R: Span of polygons

span {geosphere} | R Documentation

## Span of polygons

### Description

Compute the approximate surface span of polygons in longitude and latitude direction. Span is computed by rasterizing the polygons; and precision increases with the number of 'scan lines'. You can either use a fixed number of scan lines for each polygon, or a fixed band-width.

### Usage

    span(x, ...)

### Arguments

`x` | a SpatialPolygons* object or a 2-column matrix (longitude/latitude)
`...` | Additional arguments, see Details

### Details

The following additional arguments can be passed, to replace default values for this function

| `nbands` | Character. Method to determine the number of bands to 'scan' the polygon. Either 'fixed' or 'variable'
| `n` | Integer >= 1. If `nbands='fixed'`, how many bands should be used
| `res` | Numeric. If `nbands='variable'`, what should the bandwidth be (in degrees)?
| `fun` | Logical. A function such as mean or min. Mean computes the average span
| `r` | Numeric. Radius of the earth; default=6378137m

### Value

A list, or a matrix if a function `fun` is specified. Values are in the units of `r` (default is meter)

### Author(s)

Robert J. Hijmans

### Examples

    pol <- rbind(c(-180,-20), c(-160,5), c(-60, 0), c(-160,-60), c(-180,-20))
    plot(pol)
    lines(pol)
    # lon and lat span in m
    span(pol, fun=max)
    x <- span(pol)
    max(x$latspan)
    mean(x$latspan)
    plot(x$longitude, x$lonspan)

[Package geosphere version 1.5-5 Index]