geom_polygonraster {ggh4x}

Polygon parameterisation for rasters

Description

geom_polygonraster takes data that describes a raster with pixels of the same size and reparametrises the data as a polygon. This allows for more flexible transformations of the data, but comes at an efficiency cost.

Usage

geom_polygonraster(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = position_lineartrans(),
  ...,
  hjust = 0.5,
  vjust = 0.5,
  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)).

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.

...

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.

hjust, vjust

horizontal and vertical justification of the grob. Each justification value should be a number between 0 and 1. Defaults to 0.5 for both, centering each pixel over its data location.

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().

Details

For each pixel in a raster, makes a vertex for each of the four corner points. These coordinates can then by transformed by coord-functions such as ggplot2::coord_polar() or position-functions such as position_lineartrans(). Currently substitutes group aesthetics right before drawing in favour of pixel identifiers.

Value

A Layer ggproto object.

Aesthetics

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

• x

• y

• fill

• alpha

• group

See Also

geom_raster()

Examples

# Combining with coord_polar()
ggplot(faithfuld, aes(waiting, eruptions)) +
  geom_polygonraster(aes(fill = density)) +
  coord_polar()

# Combining with linear transformations
df <- data.frame(x = row(volcano)[TRUE],
                 y = col(volcano)[TRUE],
                 z = volcano[TRUE])

ggplot(df, aes(x, y, fill = z)) +
  geom_polygonraster(position = position_lineartrans(angle = 30,
                                                     shear = c(1, 0)))