geom_polypath: Geom polypath, a polygon filled path that can include holes.

Description

Polygons are drawn by tracing a 'path' of linked vertices and applying rule to differentiate the inside and the outside of the area traversed. The 'evenodd' rule provides the normal expected behaviour seen in simple GIS geometry and is immune to self-intersections and the orientation of the path (clockwise or anti-clockwise). The 'winding' rule behaves differently for self-intersections depending on relative orientation of the interacting paths.

Usage

geom_polypath(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  rule = "winding",
  ...
)

Value

a ggplot2 layer

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)).

stat

The statistical transformation to use on the data for this layer, either as a ggproto Geom subclass or as a string naming the stat stripped of the stat_ prefix (e.g. "count" rather than "stat_count")

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.

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().

rule

character value specifying the path fill mode: either "winding" or "evenodd", see polypath

...

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.

Details

See https://en.wikipedia.org/wiki/Even-odd_rule and https://en.wikipedia.org/wiki/Nonzero-rule for more details.

Examples

Run this code

# When using geom_polypath, you will typically need two data frames:
# one contains the coordinates of each polygon (positions),  and the
# other the values associated with each polygon (values).  An id
# variable links the two together.
# Normally this would not be created manually, but by using \code{\link{fortify}}
# to generate it from the Spatial classes in the `sp` package.

## the built-in data \code{\link{home}} uses nested data frames
library(ggplot2)
ggplot(maphome) + aes(x = x_, y = y_, group = branch_, fill = factor(object_)) +
geom_polypath()

## this is the same example built from scratch
positions = data.frame(x = c(0, 0, 46, 46, 0, 7, 13, 13, 7, 7, 18, 24,
24, 18, 18, 31, 37, 37, 31, 31, 18.4, 18.4, 18.6, 18.8, 18.8,
18.6, 18.4, 31, 31, 37, 37, 31, 0, 21, 31, 37, 46, 0, 18, 18,
24, 24, 18, 18.4, 18.6, 18.8, 18.8, 18.6, 18.4, 18.4),
y = c(0, 19, 19, 0, 0, 6, 6, 13, 13, 6, 1, 1, 12, 12, 1, 4, 4, 11, 11,
4, 6.89999999999999, 7.49999999999999, 7.69999999999999, 7.49999999999999,
6.89999999999999, 6.69999999999999, 6.89999999999999, 27, 34,
34, 24, 27, 19, 32, 27, 24, 19, 19, 1, 12, 12, 1, 1, 6.89999999999999,
6.69999999999999, 6.89999999999999, 7.49999999999999, 7.69999999999999,
 7.49999999999999, 6.89999999999999),
 id = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 2L,
 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L, 3L),
 group = c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L, 4L,
 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 5L, 5L, 5L, 6L, 6L, 6L, 6L, 6L, 7L,
 7L, 7L, 7L, 7L, 7L, 8L, 8L, 8L, 8L, 8L, 9L, 9L, 9L, 9L, 9L, 9L, 9L))

values <- data.frame(
  id = unique(positions$id),
  value = c(2, 5.4, 3)
)

#  manually merge the two together
datapoly <- merge(values, positions, by = c("id"))

# the entire house
(house <- ggplot(datapoly, aes(x = x, y = y)) + geom_polypath(aes(fill = value, group = group)))

# just the front wall (and chimney), with its three parts, the first of which has three holes
wall <- ggplot(datapoly[datapoly$id == 1, ], aes(x = x, y = y))
wall + geom_polypath(aes(fill = id, group = group))