Circles

Setup

Packages

library(ggdiagram)
library(ggplot2)
library(dplyr)
library(ggtext)
library(ggarrow)

Base Plot

To avoid repetitive code, we make a base plot:

#| label: baseplot

my_font <- "Roboto Condensed"
my_font_size <- 20
my_point_size <- 2
my_arrowhead <- arrowheadr::arrow_head_deltoid(d = 2.3, n = 100)

# my_colors <- viridis::viridis(2, begin = .25, end = .5)
my_colors <- c("#3B528B", "#21908C")

theme_set(
  theme_minimal(
    base_size = my_font_size,
    base_family = my_font) +
    theme(axis.title.y = element_text(angle = 0, vjust = 0.5)))

bp <- ggdiagram(
  font_family = my_font,
  font_size = my_font_size,
  point_size = my_point_size,
  linewidth = .5,
  theme_function = theme_minimal,
  axis.title.x =  element_text(face = "italic"),
  axis.title.y = element_text(
    face = "italic",
    angle = 0,
    hjust = .5,
    vjust = .5)) +
  scale_x_continuous(labels = signs_centered,
                     limits = c(-4, 4)) +
  scale_y_continuous(labels = signs::signs,
                     limits = c(-4, 4))

Specifying a Circle

Circles can be specified by a point at the circle’s center (x₀, y₀) and a radius r (the distance from the center to the circle’s edge).

$$(x-x_0)^2+(y-y_0)^2=r^2$$

p <- ob_point(0,0)
r <- 3
c1 <-  ob_circle(center = p, radius = r)
c1
#> <ggdiagram::ob_circle>
#> @ center: <ggdiagram::ob_point>
#>  @ x: num 0
#>  @ y: num 0
#> @ radius: num 3
#> Other props: label, alpha, color, fill, linewidth, linetype,
#>              n, area, bounding_box, circumference, diameter,
#>              length, polygon, style, tibble, geom, arc, angle_at,
#>              normal_at, tangent_at, place, point_at, aesthetics

Code

bp +
  c1 +
  ob_segment(
    c1@center,
    c1@point_at(0),
    color = my_colors[1],
    label = ob_label(paste0("*r* = ", c1@radius), angle = 0, vjust = 0)
  ) +
  c1@center@label(vjust = 1.2, plot_point = T) 

Figure 1: A circle can be specified with a center and a radius,

Point on the circle at a specific angle

It is common to need one or more points at a specific angle.

c1@point_at(degree(60))
#> <ggdiagram::ob_polar>
#> @ x    : num 1.5
#> @ y    : num 2.6
#> @ r    : num 3
#> @ theta: <ggdiagram::radian>
#>  @ radian: num 1.05
#> Other props: alpha, color, fill, shape, size, stroke, auto_label,
#>              bounding_box, centroid, length, style, tibble, xy,
#>              geom, label, place, aesthetics

Code

deg <- degree(60)

bp + 
  c1 +
  {p45 <- c1@point_at(deg)} +
  p45@label(polar_just = ob_polar(deg, 1.5)) +
  ob_segment(c1@center, p45) +
  ob_arc(radius = 1, start = degree(0), end = deg, label = deg)

Figure 2: Point on circle that is 45° from the x-axis.

Multiple points can be specified at once.

bp + 
  c1 +
  c1@point_at(degree(seq(0,340, 20)))
  

Figure 3: Points on circle 20 degrees apart.

These can be named points (e.g., north|top|above, south|bottom|below, east|right, west|left, northwest|top left|above left, southeast|bottom right|below right, north-northwest).

positions <- c("top", "bottom", "left", "right", "northeast", "north-northeast")

bp +
  c1 +
  {p <- c1@point_at(positions)} +
  ob_label(positions, p, polar_just = ob_polar(p@theta, 1.7))

The @point_at property can take angles or named positions

Placing circles

Placing circles next to each other

The place function places an object at a specified direction and distance from another object.

bp + 
  {A <- ob_circle(
    center = ob_point(-2, 0), 
    radius = 1, 
    label = ob_label("A", size = 30))} + 
  place(
    ob_circle(radius = 1.5,
           label = ob_label("B", size = 30)),
    from = A,
    where = "right",
    sep = 1)

Figure 4: Place Circle B one unit to the right of Circle A

The where argument can take degrees or named positions:

east, right, east-northeast, northeast, top right, above right, north-northeast, north, top, above, north-northwest, northwest, top left, above left, west-northwest, west, left, west-southwest, southwest, bottom left, below left, south-southwest, south, bottom, below, south-southeast, southeast, bottom right, below right, east-southeast

Multiple circles can be created at once with named directions:

bp + 
  {c3 <- ob_circle(ob_point(0, 0), radius = 1)} + 
  place(ob_circle(radius = .5), 
        from = c3, 
        where = c("northwest", 
                  "northeast", 
                  "south-southeast", 
                  "south-southwest"), 
        sep = 1)

Figure 5: Place mutliple circles using named directions

Or with numbers (degrees):

bp + 
  c3 + 
  place(ob_circle(radius = .5), 
        from = c3, 
        where = c(0, 30, -30), 
        sep = 1)

Figure 6: Place mutliple circles using degrees

With styles:

bp +
  {c4 <- ob_circle(
      radius = 1,
      color = NA,
      fill = "gray35")} +
  place(
    ob_circle(
      color = NA,
      fill = class_color(viridis::viridis(
        n = 6, 
        option = "D"))@lighten(.7)@color
    ),
    from = c4,
    where = degree(seq(0, 300, 60)),
    sep = 1
  ) 

Figure 7: Place mutliple circles with styling

Placing circles next to points and points next to circles

This works the same as placing circles next to each other. Here we create a point in the center, place six circles around it, and then place 12 points around each circle using the map_ob function to “map” objects like the map_* functions in the purrr package.

bp +
  {p1 <- ob_point(0, 0)} +
  {c6 <- place(
      x = ob_circle(
        radius = .5,
        fill = viridis::viridis(6),
        color = NA
      ),
      from = p1,
      where = degree(seq(0, 300, 60)),
      sep = 2
    )} +
  map_ob(unbind(c6),
         \(x) ob_point(color = x@fill) |>
           place(
             from = x,
             where = degree(seq(0, 330, 30)),
             sep = .5
           ))

Figure 8: Place circles around a point, and points around each circle

Placing lines next to circles

bp +
  {c7 <- ob_circle()} +
  place(ob_line(), c7, where = degree(45), sep = 1)

Figure 9: Placing a line one unit northeast of a circle

Drawing path connectors between circles

Let’s make two circles and draw an arrow path between them

bp + 
  {c1 <- ob_circle(ob_point(-2, 2), radius = 1)} + 
  {c2 <- ob_circle(ob_point(1.5,-1.5), radius = 1.5)} +
  connect(c1, c2)

Figure 10: Connect two circles

That is fine, but we often need labels and styling to make scientific diagrams. For example:

bp +
  {cthis <- ob_circle(
    ob_point(-2, 2),
    radius = 1,
    fill = my_colors[1],
    color = NA,
    label = ob_label(
      "This",
      color = "white",
      fill = NA,
      size = 35
    )
  )} + 
  {cthat <- ob_circle(
    ob_point(1.5, -1.5),
    radius = 1.5,
    fill = my_colors[2],
    color = NA,
    label = ob_label(
      "That",
      color = "white",
      fill = NA,
      size = 55
    )
  )} +
  connect(cthis, cthat, 
       resect = 2, 
       label = ob_label("Causes", size = 20, vjust = 0),
       color = "black")

Figure 11: Connect two circles with labels and styles

Paths between circles and lines

bp + 
  c1 +
  {l1 <- ob_line(slope = 2, intercept = 0)} +
  connect(c1, l1) +
  {c2 <- ob_circle(ob_point(2, -2))} + 
  connect(l1, c2)

Figure 12: Connect a circle to a line and a line to a circle