Draw a Polar Grid with Optional Labels

Adds a polar coordinate grid (circles and radial lines) to an existing plot. Optionally includes labels for radii and angles.

Usage

polarGrid(
  nr = NULL,
  ntheta = NULL,
  col = "lightgray",
  lty = "dotted",
  lwd = par("lwd"),
  rlabels = NULL,
  alabels = NULL,
  lblradians = FALSE,
  cex.lab = 1,
  las = 1,
  adj = NULL,
  dist = NULL
)

Arguments

nr

numeric or vector controlling radial grid lines:

NULL

Uses default "pretty" axis values.

single numeric

Number of radial grid lines.

numeric vector

Explicit radii at which to draw circles.

all NA

Suppress radial grid lines.

ntheta

numeric or vector controlling angular grid lines:

NULL

Uses 12 equally spaced angles.

single numeric

Number of angular divisions.

numeric vector

Explicit angles (in radians).

all NA

Suppress angular grid lines.

col

color of grid lines.

lty

line type for grid lines.

lwd

line width for grid lines.

rlabels

optional labels for radial grid lines (excluding zero). If NULL, labels are generated automatically. Use NA to suppress labels.

alabels

optional labels for angular grid lines. If NULL, labels are generated automatically (degrees or radians). Use NA to suppress labels.

lblradians

logical; if TRUE, angle labels are shown in radians, otherwise in degrees.

cex.lab

character expansion factor for labels.

las

integer controlling label orientation (as in graphics::par()).

adj

numeric vector specifying text justification.

dist

numeric distance from origin for angular labels.

Value

Invisibly returns NULL.

Details

This function is intended to be used together with polar plotting functions such as plotPolar. It assumes an existing plot with equal aspect ratio.

Radial grid lines are drawn as concentric circles, while angular grid lines are drawn as segments from the origin.

Label placement and formatting can be customized via adj, las, and dist.

See also

grid()

Other graphics.setup: canvas(), setBackCol()

Examples

plot(0, 0, type = "n", xlim = c(-1, 1), ylim = c(-1, 1), asp = 1)
polarGrid()


# custom grid
plot(0, 0, type = "n", xlim = c(-2, 2), ylim = c(-2, 2), asp = 1)
polarGrid(nr = 4, ntheta = 8, col = "gray")

# suppress labels
polarGrid(rlabels = NA, alabels = NA)