scale_coltab {tidyterra}

Discrete scales based in the color table of a SpatRaster

Description

Some categorical SpatRaster objects may have an associated color table. This function extract those values. These functions generates scales and vector of colors based on the color table terra::coltab() associated to a SpatRaster.

You can also get a vector of colors named with the corresponding factor with get_coltab_pal().

Additional parameters ... would be passed on to ggplot2::discrete_scale().

Note that tidyterra just documents a selection of these additional parameters, check ggplot2::discrete_scale() to see the full range of parameters accepted.

Usage

scale_fill_coltab(
  data,
  ...,
  alpha = 1,
  na.translate = FALSE,
  na.value = "transparent",
  drop = TRUE
)

scale_colour_coltab(
  data,
  ...,
  alpha = 1,
  na.translate = FALSE,
  na.value = "transparent",
  drop = TRUE
)

get_coltab_pal(x)

Arguments

data, x

A SpatRaster with one or several color tables. See terra::has.colors().

...

Arguments passed on to ggplot2::discrete_scale

breaks

One of:

• NULL for no breaks

• waiver() for the default breaks (the scale limits)

• A character vector of breaks

• A function that takes the limits as input and returns breaks as output. Also accepts rlang lambda function notation.

labels

One of:

• NULL for no labels

• waiver() for the default labels computed by the transformation object

• A character vector giving labels (must be same length as breaks)

• An expression vector (must be the same length as breaks). See ?plotmath for details.

• A function that takes the breaks as input and returns labels as output. Also accepts rlang lambda function notation.

limits

One of:

• NULL to use the default scale values

• A character vector that defines possible values of the scale and their order

• A function that accepts the existing (automatic) values and returns new ones. Also accepts rlang lambda function notation.

expand

For position scales, a vector of range expansion constants used to add some padding around the data to ensure that they are placed some distance away from the axes. Use the convenience function expansion() to generate the values for the expand argument. The defaults are to expand the scale by 5% on each side for continuous variables, and by 0.6 units on each side for discrete variables.

alpha

The alpha transparency, a number in [0,1], see argument alpha in hsv.

na.translate

Should NA values be removed from the legend? Default is TRUE.

na.value

Missing values will be replaced with this value. By default, tidyterra uses na.value = "transparent" so cells with NA are not filled. See also #120.

drop

Should unused factor levels be omitted from the scale? The default (TRUE) removes unused factors.

Value

The corresponding ggplot2 layer with the values applied to the fill/colour aesthetics.

See Also

terra::coltab(), ggplot2::discrete_scale(), ggplot2::scale_fill_manual(),

Examples

library(terra)
# Geological Eras
# Spanish Geological Survey (IGME)

r <- rast(system.file("extdata/cyl_era.tif", package = "tidyterra"))

plot(r)

# Get coltab
coltab_pal <- get_coltab_pal(r)

coltab_pal


# With ggplot2 + tidyterra
library(ggplot2)

gg <- ggplot() +
  geom_spatraster(data = r)


# Default plot
gg

# With coltabs
gg +
  scale_fill_coltab(data = r)