latitudecircle {spex}

Latitude circle

Description

Create a circular polygon using a latitude value in a map projection. The longitude range can be modified from global to give a portion of a circle.

Usage

latitudecircle(
  latitude = 0,
  crs = "+proj=stere +lon_0=0 +lat_0=-90 +lat_ts=-71 +ellps=WGS84",
  lonlim = c(-180, 180),
  nverts = 1800
)

Arguments

latitude

latitude value for the boundary, defaults to 0

crs

map projection to use, defaults to southern Polar Stereographic true scale at -71S

lonlim

the range of longitude to use, defaults to entire globe

nverts

total number of vertices to use, see Details

Details

The argument nverts controls the total number of vertices of the circle within a linearly within the lonlim range of longitudes at latitude

This is for use on classic polar projections centred on the north or the south pole, particularly Polar Stereographic and Lambert Azimuthal Equal Area but will also work with some caveats on other families and situations. We have not explored this more general use. Feel free to contact the maintainer if you have interest in less typical usage or find problems.

Value

SpatialPolygonsDataFrame

Examples

latitudecircle(seq(0, -65, by = -5))
library(raster)
plot(ice)
circ <- latitudecircle(-71, crs = projection(ice))
plot(circ, add = TRUE)