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Apply Chaikin's corner cutting algorithm to smooth a path

Source: R/geom-chaikin.R, R/stat_chaikin.R
geom_chaikin.Rd

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",
  ...,
  iterations = 5,
  ratio = 0.25,
  closed = FALSE,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_chaikin(
  mapping = NULL,
  data = NULL,
  geom = "path",
  position = "identity",
  ...,
  iterations = 5,
  ratio = 0.25,
  closed = FALSE,
  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

Position adjustment, either as a string naming the adjustment (e.g. "jitter" to use position_jitter), or the result of a call to a position adjustment function. Use the latter if you need to change the settings of the adjustment.

...

Other arguments passed on to layer(). These are often aesthetics, used to set an aesthetic to a fixed value, like colour = "red" or size = 3. They may also be parameters to the paired geom/stat.

iterations

Integer. Number of iterations to apply. Must be between 0 and 10.

ratio

Numeric. Cutting ratio must be between 0 and 1.

closed

Logical. Specify if result is an open or closed shape.

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.

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. borders().

geom, stat

Use to override the default connection between geom_chaikin and stat_chaikin.

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.

The ratio parameter must be a number between 0 and 1. If ratio > 0.5, then it will be flipped to 1 - ratio, and a message is shown.

Aesthetics

geom_chaikin() understands the following aesthetics (required aesthetics are in bold):

  • x

  • y

  • alpha

  • color

  • group

  • linetype

  • linewidth

References

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

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 let's you control
p2 + geom_chaikin(ratio = .1)

p2 + geom_chaikin(ratio = .5)


# closed parameter to generate a closed shape - or not
p2 + geom_chaikin(iterations = 5, ratio = 0.25, closed = FALSE) # default

p2 + geom_chaikin(closed = TRUE)