Apply Chaikin's corner cutting algorithm to smooth a path

Chaikin's corner-cutting algorithm can be used to smooth sharp corners of a path.

Usage

geom_chaikin(
  mapping = NULL,
  data = NULL,
  stat = "chaikin",
  position = "identity",
  ...,
  mode = "open",
  iterations = 5,
  ratio = 0.25,
  arrow = NULL,
  arrow.fill = NULL,
  lineend = "butt",
  linejoin = "round",
  linemitre = 10,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_chaikin(
  mapping = NULL,
  data = NULL,
  geom = "path",
  position = "identity",
  ...,
  mode = "open",
  iterations = 5,
  ratio = 0.25,
  closed = lifecycle::deprecated(),
  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.

mode

Character. Should the geom draw a closed polygon or an open path? Must be one of "open" (default) or "closed".

iterations

Integer. Number of iterations to apply between 1 and 10. When iterations = 0 the original data is unchanged so essentially this is the same as calling ggplot2::geom_path(); however this might be useful when you want to toggle smoothing on/off programmatically without removing the layer.

ratio

Numeric. Cutting ratio must be a number between 0 and 1. If ratio > 0.5, then it will be flipped to 1 - ratio.

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).

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().

geom, stat

Use to override the default connection between geom_chaikin() and stat_chaikin().

closed

Use mode instead.

Value

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

Details

Chaikin's corner cutting algorithm iteratively turns a jagged path into a smooth path.

The recursion formula starts from two vertices A and B, which represent a single corner of your path. From this, the algorithm derives two new points: one at the specified ratio when going from point A to point B, and one when going from B to A in the opposite direction. By default, a ratio of 0.25 results in two points: the first at 25% of point A and the other at 75% of point A (or 25% of point B). Those new points form a smoother path. Then the algorithm applies the same rule to each pair of new points. The rule is applied iterations times. The maximum number of iterations is 10, default is 5.

References

Chaikin, G. An algorithm for high speed curve generation. Computer Graphics and Image Processing 3 (1974), 346–349

Aesthetics

geom_chaikin() 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

set.seed(42)
dat <- data.frame(
  x = seq.int(10),
  y = sample(15:30, 10)
)

p1 <- ggplot(dat, aes(x, y)) +
  geom_line(linetype = "12")

p1 +
  geom_chaikin()


p1 +
  geom_chaikin(iterations = 1)


triangle <- data.frame(x = c(0, 0, 1), y = c(0, 1, 1))
p2 <- ggplot(triangle, aes(x, y)) +
  geom_path(linetype = "12") +
  coord_equal()

# ratio lets you control the cutting amount
p2 + geom_chaikin(ratio = .1)

p2 + geom_chaikin(ratio = .5)


# mode controls whether the result is an open or closed shape
p2 + geom_chaikin(mode = "open")   # default

p2 + geom_chaikin(mode = "closed")