geosphere (version 1.5-18)

span: 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, ...)

Value

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

Arguments

x

a SpatialPolygons* object or a 2-column matrix (longitude/latitude)

...

Additional arguments, see Details

Author

Robert J. Hijmans

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
	...	further additional arguments passed to distGeo

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)