sl.circle: Compute Points Approximating a Circle on a Sphere

In helgegoessling/spheRlab: Spherical Geometry, Analysis, and Plotting of Geoscientific Data on Arbitrary Grids

Compute Points Approximating a Circle on a Sphere

Description

Compute points approximating a circle on a sphere around a central location. Points are placed equidistant on a circle around a central longitude-latitude location with a to-be-specified radius.

Usage

sl.circle(lon, lat, radius, resolution = 1, repeat.first = TRUE)

Arguments

lon	a scalar specifying the central longitude.
lat	a scalar specifying the central latitude.
radius	a scalar specifying the radius in degrees.
resolution	a scalar specifying the resolution (distance between points) in degrees (around the central point).
repeat.first	a logical value specifying whether to close the circle explicitly by repeating the first point at the end.

Value

lon	Longitudes of the points on the circle
lat	Latitudes of the points on the circle

Author(s)

Helge Goessling

Examples

sl.circle(lon = 8, lat = 50, radius = 5, resolution=30)
# should return:
#$lon
# [1] 15.7507972 15.0886911 12.2782746  8.0000000  3.7217254  0.9113089  0.2492028  1.6076588
# [9]  4.4283457  8.0000000 11.5716543 14.3923412 15.7507972 15.7507972
#
#$lat
# [1] 49.74086 52.29224 54.25711 55.00000 54.25711 52.29224 49.74086 47.31720 45.61144 45.00000
#[11] 45.61144 47.31720 49.74086 49.74086

# Now some nice 'circles' on a lonlat plot:
pir = sl.plot.init(projection="lonlat",do.init.device=FALSE)
res = sl.plot.naturalearth(pir,resolution="coarse")

circ = sl.circle(90,-30,40)
sl.plot.lines(pir,circ$lon,circ$lat,col="blue")

circ = sl.circle(-30,70,25)
sl.plot.lines(pir,circ$lon,circ$lat,col="red")

sl.plot.end(pir,do.close.device=FALSE)

helgegoessling/spheRlab documentation built on July 14, 2024, 4:56 p.m.