ggpolypath: Polygons with Holes for the Grammar of Graphics

Description

Tools for working with polygons with holes in 'ggplot2', with a new 'geom' for drawing a 'polypath' applying the 'evenodd' or 'winding' rules.

Tools for working with polygons with holes in 'ggplot2', with a new 'geom' for drawing a 'polypath' applying the 'evenodd' or 'winding' rules.

Author(s)

Maintainer: Michael D. Sumner mdsumner@gmail.com

Other contributors:

• Kohske Takahashi takahashi.kohske@gmail.com (original author of 'geom_holygon') [contributor]

See Also

Useful links:

• https://mdsumner.github.io/ggpolypath/

• http://rpubs.com/kohske/3522/

• Report bugs at https://github.com/mdsumner/ggpolypath/issues/

Simple polygon data

Description

A "home" profile of three objects with multiple parts as two related data frames.

Format

dathome is the metadata, a data frame with columns:

name

A descriptive name

colour

A colour to distinguish each object

FAD

An arbitrary numeric value

object_

Key attribute, linking this object to its geometry in maphome

maphome is the geometry, a data frame with columns:

object_

Key attribute, linking this row to its metadata in dathome

branch_

Group attribute, unique values identify a closed ring

island_

Logical, TRUE for "island" vs. "hole"

order_

Numeric value to identify sort order within branch

x_,y_

x and y coordinate

Details

maphome is the geometry

Examples

ggplot(maphome) + aes(x = x_, y = y_, group = branch_, fill = object_) +
geom_polypath() + geom_path() + facet_wrap(~object_, nrow = nrow(dathome))

Province polygons with inland waters as holes.

Description

A data frame of coordinates and geometry classifiers of the garden state, South Australia.

Format

gardenstate is the geometry, a data frame with columns:

x,y

x and y coordinate

id

Key attribute for the objects

piece,part

Group attribute, unique values identify a closed ring, part is the part 'id' within an object

hole

Logical, FALSE for "island" vs. "hole"

order

Numeric value to identify sort order within branch

Details

The PROJ.4 string for this map is:

+proj=lcc +lat_1=-47 +lat_2=-17 +lat_0=-32 +lon_0=136 +x_0=0 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs

Examples

gs <- ggplot(gardenstate)
gs <- gs + aes(x = x, y = y, group = group, fill = id)
gs +  geom_polypath() + geom_path()

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",
  ...
)

Arguments

Details

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

Value

a ggplot2 layer

See Also

polypath and pathGrob geom_polygon for the implementation on polygonGrob, geom_map for a convenient way to tie the values and coordinates together, geom_path for an unfilled polygon, geom_ribbon for a polygon anchored on the x-axis

Examples

# 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))