Dear R-users,
Hereby a polar plot function for plotting angular data. I hope it will be
usefull for some of you.
I had a need to plot frequencies of wind-directions. The not-that-cheap
SigmaPlot software did not allow me to change the orientation of the angular
axis to clockwise orientation (what is used for meteorological observations). I
even tried the latest version availible at the time (late 2001), but I did not
succed. Returning to my own computer with newly saved SP-files, however, I was
not able to open them. This is one of many reasons why open-source software is
such a good alternative!
After making my polar plots, I spend some time making the code more flexible.
As I am a "learning by doing" R-programmer, the code may benefit from
further development - particulary for adjustment to general R-language
conventions for plot-functions.
If possible, it would be nice to have a polar plot function as a more permanent
part of R!
Thanks to Ross Ihaka at R-help (Mon May 28 2001) for some of the polar.plot code
used.
Best wishes,
Karsten
#########
"polar.plot" <-
function (r, theta, theta.zero = 0, theta.clw = FALSE, method = 1,
rlabel.axis = 0, dir = 8, rlimits = NULL, grid.circle.pos = NULL,
grid.lwd = 1, grid.col = "black", points.pch = 20, points.cex = 1,
lp.col = "black", lines.lwd = 1, lines.lty = 1, polygon.col = NA,
polygon.bottom = TRUE, overlay = NULL, pi2.lab = TRUE, text.lab = NULL,
num.lab = NULL, rlabel.method = 1, rlabel.pos = 3, rlabel.cex = 1,
rlabel.col = "black", tlabel.offset = 0.1, tlabel.cex = 1.5,
tlabel.col = "black", main = NULL, sub = NULL)
{
# r: (vector of) radial data.
# theta: (vector of) angular data (in radians).
# theta.zero: angular direction on plot of theta = 0 (in radians).
# theta.clw: clockwise orientation of theta values (default = FALSE).
#
# method: (plotting of (r,theta)-data):
# 1: points (default)
# 2: line
# 3: polygon
#
# rlabel.axis: angular direction on the plot of radial label axis (in radians).
# dir: number of radial grid lines (default=8).
# rlimts: Interval for radial axis as a numeric vector: c(lower,upper). Interval
will be extended by the default use of pretty()-function. (default = NULL).
# grid.circle.pos: radial axis position of grid circles as numeric vector of
minimum length 2. Overrides the default positioning of grid circles by
pretty()-function. (default = NULL).
# grid.lwd. grid line width.
# grid.col: grid line color.
#
# points.pch: points plotting symbol.
# point.cex: character expansion factor for points.
# lp.col: color of points (method 1) or lines (method 2 and method 3). In method
3, set lp.col=0 for polygons without border.
# lines.lwd: line width for plotting methods 2 and 3 (default = 1).
# lines.lty: line type (default = 1).
# polygon.col: color of polygon (defalut = NA).
# polygon.bottom: polygon to the back i.e. behind the grid (default = TRUE).
#
# overlay: NULL (default), no overlay
# 1, overlay data on existing plot
# 2, overlay data, grid and labels on existing plot.
#
# pi2.lab: angular labels in radians (0, pi/2, pi, 3*pi/2) (default).
# text.lab: angular axis labels from a character vector
c("N","E","S","W") (default = NULL).
# num.lab: numeric angular axis labels in interval [0;num.lab[ (default =
NULL). Number of labels: dir.
#
# rlabel.method (plotting of radial axis labels):
# 0: no radial labels.
# 1: labels at pretty radial distances (default).
# 2: exclude label at radial distace 0.
# 3: exclude label at maximum radial distance.
# 4: exclude radial labels at distance 0 and at maximum radial distance.
# rlabel.pos: text position of radial axis labels (NULL,1,2,3,4).
# rlabel.cex: cex for radial axis labels.
# rlabel.col: color of the radial labels.
#
# tlabel.offset: radial offset for angular axis labels in fraction of maximum
radial value (default = 0.1).
# tlabel.cex: cex for angular axis labels.
# tlabel.col: angular labels color.
#
# main: plot main title.
# sub: plot sub title.
fit.rad <- function(x, twop = 2 * pi) {
for (i in 1:length(x)) {
while (x[i] < 0) x[i] <- x[i] + twop
while (x[i] >= twop) x[i] <- x[i] - twop
}
return(x)
}
if (is.null(rlimits))
rpretty <- pretty(range(abs(r), 0, na.rm = TRUE))
if (is.numeric(rlimits) & length(rlimits) == 2)
rpretty <- pretty(range(abs(rlimits[1]), abs(rlimits[2])))
if (is.numeric(grid.circle.pos) & length(grid.circle.pos) >
1)
rpretty <- grid.circle.pos
lab.dist <- max(rpretty)
if (!is.null(text.lab) || is.numeric(num.lab) || pi2.lab) {
lab.dist <- lab.dist * (tlabel.offset + 1)
}
if (is.null(overlay)) {
plot.new()
ps <- max(lab.dist, max(rpretty))
plot.window(xlim = c(-ps, ps), ylim = c(-ps, ps), asp = 1)
title(main = main, sub = sub)
}
drawgrid <- function() {
if (dir > 0) {
rDir <- seq(0, 2 * pi, length = dir + 1)[-(dir +
1)]
segments(0, 0, max(rpretty) * cos(rDir), max(rpretty) *
sin(rDir), col = grid.col, lwd = grid.lwd)
}
grid <- seq(0, 2 * pi, length = 360/4 + 1)
for (rad in rpretty) {
if (rad > 0)
lines(rad * cos(grid), rad * sin(grid), col = grid.col,
lwd = grid.lwd)
}
if (rlabel.method != 0) {
if (rlabel.method == 1)
radLabels <- 1:length(rpretty)
if (rlabel.method == 2)
radLabels <- 2:length(rpretty)
if (rlabel.method == 3)
radLabels <- 1:(length(rpretty) - 1)
if (rlabel.method == 4) {
if (length(rpretty) > 2)
radLabels <- 2:(length(rpretty) - 1)
else radLabels <- NULL
}
if (!is.null(radLabels)) {
xpos <- rpretty[radLabels] * cos(rlabel.axis)
ypos <- rpretty[radLabels] * sin(rlabel.axis)
text(xpos, ypos, rpretty[radLabels], cex = rlabel.cex,
pos = rlabel.pos, col = rlabel.col)
}
}
if (!is.numeric(num.lab)) {
if (pi2.lab & !is.character(text.lab))
t.lab <- expression(0, pi/2, pi, 3 * pi/2)
if (!pi2.lab & is.character(text.lab))
t.lab <- text.lab
labDir <- seq(0, 2 * pi, length = length(t.lab) +
1)[-(length(t.lab) + 1)]
labDir <- fit.rad(theta.zero + (!theta.clw) * labDir -
(theta.clw) * labDir)
text(lab.dist * cos(labDir), lab.dist * sin(labDir),
t.lab, cex = tlabel.cex, col = tlabel.col)
}
if (!pi2.lab & is.null(text.lab) & is.numeric(num.lab)) {
labDir <- seq(0, 2 * pi, length = num.lab + 1)[-(num.lab +
1)]
labDir <- fit.rad(theta.zero + (!theta.clw) * labDir -
(theta.clw) * labDir)
text(lab.dist * cos(labDir), lab.dist * sin(labDir),
paste(num.lab * labDir/(2 * pi)), cex = tlabel.cex,
col = tlabel.col)
}
if ((is.character(text.lab) & is.numeric(num.lab)) ||
(is.character(text.lab) & pi2.lab) || (pi2.lab &
is.numeric(num.lab)))
print("More than one type of angular labels was
requested.")
}
theta2 <- fit.rad(theta.zero + (!theta.clw) * theta - (theta.clw) *
theta)
cartesian.rt <- cbind(r * cos(theta2), r * sin(theta2))
if (method == 1) {
if (is.null(overlay) || overlay == 2)
drawgrid()
points(cartesian.rt[, 1], cartesian.rt[, 2], col = lp.col,
pch = points.pch, cex = points.cex)
}
if (method == 2) {
if (is.null(overlay) || overlay == 2)
drawgrid()
lines(cartesian.rt[, 1], cartesian.rt[, 2], lwd = lines.lwd,
col = lp.col, lty = lines.lty)
}
if ((method == 2 || method == 3) & length(r) <= 1)
print("More than one data point is needed for line and polygon
methods.")
if (method == 3) {
if (!polygon.bottom & (is.null(overlay) || overlay ==
2))
drawgrid()
polygon(cartesian.rt, lwd = lines.lwd, col = polygon.col,
border = lp.col, lty = lines.lty)
if (polygon.bottom & (is.null(overlay) || overlay ==
2))
drawgrid()
}
}
###########################
# data
div<-50
theta <- seq(0, 2 * pi, length = div + 1)[-(div+1)]
r<-1:(div)
r2<-rep(12,times=div)
r3<-rep(32,times=div)
# use of polar.plot
polar.plot(9, pi/4, dir = 4, points.cex = 1.5)
polar.plot(r, theta)
polar.plot(r, theta, method = 2, lines.lwd = 3, lines.lty=2, lp.col =
"blue")
polar.plot(r, theta, method=3, pi2.lab = FALSE, dir = 7, lines.lwd = 3,
polygon.col="blue", lp.col = "red", grid.circle.pos = c(0,
50), rlabel.method=4 )
# overlay of polar plots
polar.plot(r3, theta, method = 3, rlimits=c(0,50), rlabel.method = 2, lp.col =
0, polygon.col = "blue")
polar.plot(r2, theta, method = 3, overlay=1, lp.col = 0, polygon.col =
"white")
polar.plot(r/2+15, 2*theta, lp.col = "red", method = 1,
rlimits=c(0,50), overlay =2, points.cex = 1.5)
title(main="Overlay red points on white polygon on blue polygon")
# theta axis labels as text
textlabels<-c('N','E','S','W')
polar.plot(r, theta, theta.clw = TRUE, theta.zero = pi/2, text.lab = textlabels
, pi2.lab = FALSE, lines.lwd = 3, grid.lwd = 1, grid.col =
"darkgreen", rlabel.method = 2, rlabel.axis = -pi/2, rlabel.cex = 2,
rlabel.pos = NULL, rlabel.col = "brown", tlabel.col =
"darkgreen", points.cex = 3, points.pch = 21, tlabel.cex = 3,
tlabel.offset = 0.3, lp.col = "red")
title(main="A Compas Rose\n Hurray for the R core group!")
# Example by Ross Ihaka at R-help
group <- sample(3, 100, replace = TRUE)
theta <- 0.5 * rnorm(100) + 0.5 * group
r <- rnorm(100, 4)
polar.plot(r, theta, lp.col =
c("red","green4","blue")[group], points.pch = 19)
---ooo---
Karsten Dalsgaard Bjerre (M.Sc. Agriculture, Ph.D. Student).
Department of Plant Biology
Royal Veterinary and Agricultural University
40 Thorvaldsensvej
DK-1871 Frederiksberg C
Denmark
Tel: (+45) 3528 3418
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