Catenary Curves and Arches

geom_catenary() draws a catenary curve (hanging chain) between successive points. geom_arch() draws an inverted catenary curve and is hence intended for people living on the southern hemisphere.

The shape follows the catenary equation: \(\ y = a\ \cosh \ \!\bigl(\frac{x - h}{a}\bigr) + v\).

Usage

geom_catenary(
  mapping = NULL,
  data = NULL,
  stat = "catenary",
  position = "identity",
  ...,
  chain_length = NULL,
  sag = NULL,
  chainLength = lifecycle::deprecated(),
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

geom_arch(
  mapping = NULL,
  data = NULL,
  stat = "arch",
  position = "identity",
  ...,
  arch_length = NULL,
  arch_height = NULL,
  arrow = NULL,
  arrow.fill = NULL,
  lineend = "butt",
  linejoin = "round",
  linemitre = 10,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_catenary(
  mapping = NULL,
  data = NULL,
  geom = "catenary",
  position = "identity",
  ...,
  chain_length = NULL,
  sag = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_arch(
  mapping = NULL,
  data = NULL,
  geom = "line",
  position = "identity",
  ...,
  arch_length = NULL,
  arch_height = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.
A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".
For more information and other ways to specify the position, see the layer position documentation.

...

Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored.

Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data.
When constructing a layer using a stat_*() function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept.
Inversely, when constructing a layer using a geom_*() function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept.
The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.

chain_length

Numeric vector of physical chain lengths. Recycled to the number of segments. If NULL and sag is also NULL, defaults to twice the Euclidean distance per segment. Can be mixed with sag by placing NA in the appropriate positions.

sag

Numeric vector giving the vertical drop of the curve below the lowest endpoint of each segment. Takes precedence over chain_length when both are supplied for the same segment.

chainLength

Use chain_length instead.

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

arch_length

Numeric vector of arch lengths. Recycled to the number of segments. If NULL and arch_height is also NULL, defaults to twice the Euclidean distance per segment. Can be mixed with arch_height by placing NA in the appropriate positions.

arch_height

Numeric vector giving the vertical rise of the arch above the highest endpoint of each segment. Takes precedence over arch_length when both are supplied for the same segment.

arrow

Arrow specification, as created by grid::arrow().

arrow.fill

fill colour to use for the arrow head (if closed). NULL means use colour aesthetic.

lineend

Line end style (round, butt, square).

linejoin

Line join style (round, mitre, bevel).

linemitre

Line mitre limit (number greater than 1).

geom, stat

Override the default connection between geom_catenary() and stat_catenary(), or between geom_arch() and stat_arch().

Value

A ggplot2::layer() object that can be added to a ggplot2::ggplot().

Aesthetics

geom_catenary() understands the following aesthetics. Required aesthetics are displayed in bold and defaults are displayed for optional aesthetics:

•	`x`
•	`y`
•	`alpha`	→ `NA`
•	`colour`	→ via `theme()`
•	`group`	→ inferred
•	`linetype`	→ via `theme()`
•	`linewidth`	→ via `theme()`

Learn more about setting these aesthetics in vignette("ggplot2-specs").

Examples

library(ggplot2)

df <- data.frame(x = seq_len(4), y = c(1, 1, 0, 2))

# basic usage
p <- ggplot(df, aes(x, y)) + ylim(-3, NA) + geom_point(size = 3)
p + geom_catenary()


# Catenary with sag = 2, considered from lowest point of each segment
# recycled, if only a one value is provided
p + geom_catenary(sag = 2)

p + geom_catenary(sag = c(2, 1, 1))


# if sag and chain_length are provided for same segment(s), sag wins
p + geom_catenary(sag = c(2, 1, NA), chain_length = 10)
#> Both `sag` and `chain_length` supplied for 2 segments; using `sag`.
#> This message is displayed once every 8 hours.


# Arch with height = 2, considered from highest point of each segment
p + geom_arch(arch_height = c(2, 1, 1))


# Rice house, see https://en.wikipedia.org/wiki/Rice_House,_Eltham
rice_house <- data.frame(x = c(0, 1.5, 2.5, 3.5, 5), y = c(0, 1, 1, 1, 0))
ggplot(rice_house, aes(x, y)) +
  geom_arch(arch_height = .15, lwd = 2) +
  geom_segment(aes(xend = x, yend = 0)) +
  geom_hline(yintercept = 0, colour = "forestgreen", linewidth = 3) +
  coord_equal()

Usage

Arguments

Value

See also

Aesthetics

Examples