Connect control points/observations with an X-spline

Share:

Description

Draw an X-spline, a curve drawn relative to control points/observations. Patterned after geom_line in that it orders the points by x first before computing the splines.

Usage

1
2
3
4
5
6
7
8
9
geom_xspline(mapping = NULL, data = NULL, stat = "xspline",
  position = "identity", na.rm = TRUE, show.legend = NA,
  inherit.aes = TRUE, spline_shape = -0.25, open = TRUE,
  rep_ends = TRUE, ...)

stat_xspline(mapping = NULL, data = NULL, geom = "line",
  position = "identity", na.rm = TRUE, show.legend = NA,
  inherit.aes = TRUE, spline_shape = -0.25, open = TRUE,
  rep_ends = TRUE, ...)

Arguments

mapping

Set of aesthetic mappings created by aes or aes_. If specified and inherit.aes = TRUE (the default), is combined with the default mapping at the top level of the plot. You only need to supply mapping if there isn't a mapping defined for the plot.

data

A data frame. If specified, overrides the default data frame defined at the top level of the plot.

position

Position adjustment, either as a string, or the result of a call to a position adjustment function.

na.rm

If FALSE (the default), removes missing values with a warning. If TRUE silently removes missing values.

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.

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.

spline_shape

A numeric vector of values between -1 and 1, which control the shape of the spline relative to the control points.

open

A logical value indicating whether the spline is an open or a closed shape.

rep_ends

For open X-splines, a logical value indicating whether the first and last control points should be replicated for drawing the curve. Ignored for closed X-splines.

...

other arguments passed on to layer. There are three types of arguments you can use here:

  • Aesthetics: to set an aesthetic to a fixed value, like color = "red" or size = 3.

  • Other arguments to the layer, for example you override the default stat associated with the layer.

  • Other arguments passed on to the stat.

geom, stat

Use to override the default connection between geom_xspline and stat_xspline.

Details

A sample of the output from geom_xspline():

Figure: geom\_xspline\_01.png

An X-spline is a line drawn relative to control points. For each control point, the line may pass through (interpolate) the control point or it may only approach (approximate) the control point; the behaviour is determined by a shape parameter for each control point.

If the shape parameter is greater than zero, the spline approximates the control points (and is very similar to a cubic B-spline when the shape is 1). If the shape parameter is less than zero, the spline interpolates the control points (and is very similar to a Catmull-Rom spline when the shape is -1). If the shape parameter is 0, the spline forms a sharp corner at that control point.

For open X-splines, the start and end control points must have a shape of 0 (and non-zero values are silently converted to zero).

For open X-splines, by default the start and end control points are replicated before the curve is drawn. A curve is drawn between (interpolating or approximating) the second and third of each set of four control points, so this default behaviour ensures that the resulting curve starts at the first control point you have specified and ends at the last control point. The default behaviour can be turned off via the repEnds argument.

Aesthetics

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

  • x

  • y

  • alpha

  • color

  • linetype

  • size

Computed variables

  • x

  • y

References

Blanc, C. and Schlick, C. (1995), "X-splines : A Spline Model Designed for the End User", in Proceedings of SIGGRAPH 95, pp. 377-386. http://dept-info.labri.fr/~schlick/DOC/sig1.html

See Also

geom_line: Connect observations (x order); geom_path: Connect observations; geom_polygon: Filled paths (polygons); geom_segment: Line segments; xspline; grid.xspline

Examples

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
set.seed(1492)
dat <- data.frame(x=c(1:10, 1:10, 1:10),
                  y=c(sample(15:30, 10), 2*sample(15:30, 10),
                      3*sample(15:30, 10)),
                  group=factor(c(rep(1, 10), rep(2, 10), rep(3, 10)))
)

ggplot(dat, aes(x, y, group=group, color=group)) +
  geom_point() +
  geom_line()

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point() +
  geom_line() +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(spline_shape=-0.4, size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(spline_shape=0.4, size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(spline_shape=1, size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(spline_shape=0, size=0.5)

ggplot(dat, aes(x, y, group=group, color=factor(group))) +
  geom_point(color="black") +
  geom_smooth(se=FALSE, linetype="dashed", size=0.5) +
  geom_xspline(spline_shape=-1, size=0.5)