Skip to contents

Plot RGB rasters in ggplot2

Source: R/geom_spatial_rgb.R
geom_spatial_rgb.Rd

geom_spatial_rgb and stat_spatial_rgb allow users to plot three-band RGB rasters in ggplot2, using these layers as background base maps for other spatial plotting. Note that unlike ggplot2::geom_sf, this function does not force ggplot2::coord_sf; for accurate mapping, add ggplot2::coord_sf with a crs value matching your input raster as a layer.

Usage

geom_spatial_rgb(
  mapping = NULL,
  data = NULL,
  stat = "spatialRGB",
  position = "identity",
  ...,
  hjust = 0.5,
  vjust = 0.5,
  interpolate = FALSE,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  scale = NULL
)

stat_spatial_rgb(
  mapping = NULL,
  data = NULL,
  geom = "raster",
  position = "identity",
  na.rm = FALSE,
  show.legend = FALSE,
  inherit.aes = TRUE,
  scale = NULL,
  ...
)

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. In addition to the three options described in ggplot2::geom_raster, there are two additional methods:

If a SpatRaster object (see terra::rast), this function will coerce the raster to a data frame and assume the raster bands are in RGB order (while allowing for, but ignoring, a fourth alpha band).

If a length-1 character vector, this function will attempt to load the object via terra::rast.

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used the override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

  • For more information and other ways to specify the stat, see the layer stat documentation.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

...

Other arguments passed on to layer()'s params argument. These arguments broadly fall into one of 4 categories below. Notably, further arguments to the position argument, or aesthetics that are required can not be passed through .... Unknown arguments that are not part of the 4 categories below are ignored.

  • Static aesthetics that are not mapped to a scale, but are at a fixed value and apply to the layer as a whole. For example, colour = "red" or linewidth = 3. The geom's documentation has an Aesthetics section that lists the available options. The 'required' aesthetics cannot be passed on to the params. Please note that while passing unmapped aesthetics as vectors is technically possible, the order and required length is not guaranteed to be parallel to the input data.

  • When constructing a layer using a stat_*() function, the ... argument can be used to pass on parameters to the geom part of the layer. An example of this is stat_density(geom = "area", outline.type = "both"). The geom's documentation lists which parameters it can accept.

  • Inversely, when constructing a layer using a geom_*() function, the ... argument can be used to pass on parameters to the stat part of the layer. An example of this is geom_area(stat = "density", adjust = 0.5). The stat's documentation lists which parameters it can accept.

  • The key_glyph argument of layer() may also be passed on through .... This can be one of the functions described as key glyphs, to change the display of the layer in the legend.

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.

interpolate

If TRUE interpolate linearly, if FALSE (the default) don't interpolate.

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().

scale

Integer. Maximum (possible) value in the three channels. If NULL, attempts to infer proper values from data – if all RGB values are <= 1 then 1, <= 255 then 255, and otherwise 65535.

geom

The geometric object to use to display the data for this layer. When using a stat_*() function to construct a layer, the geom argument can be used to override the default coupling between stats and geoms. The geom argument accepts the following:

  • A Geom ggproto subclass, for example GeomPoint.

  • A string naming the geom. To give the geom as a string, strip the function name of the geom_ prefix. For example, to use geom_point(), give the geom as "point".

  • For more information and other ways to specify the geom, see the layer geom documentation.

See also

Other visualization functions: combine_overlays(), raster_to_raw_tiles(), vector_to_overlay()

Examples

if (FALSE) { # \dontrun{

simulated_data <- data.frame(
  id = seq(1, 100, 1),
  lat = runif(100, 44.04905, 44.17609),
  lng = runif(100, -74.01188, -73.83493)
)

simulated_data <- sf::st_as_sf(simulated_data, coords = c("lng", "lat"))
simulated_data <- sf::st_set_crs(simulated_data, 4326)

output_tiles <- get_tiles(simulated_data,
  services = c("ortho"),
  resolution = 120
)

merged_ortho <- tempfile(fileext = ".tif")
merge_rasters(output_tiles[["ortho"]], merged_ortho)

merged_stack <- terra::rast(merged_ortho)

library(ggplot2)

ggplot() +
  geom_spatial_rgb(
    data = merged_ortho,
    mapping = aes(
      x = x,
      y = y,
      r = red,
      g = green,
      b = blue
    )
  ) +
  geom_sf(data = simulated_data) +
  coord_sf(crs = 4326)

ggplot() +
  geom_spatial_rgb(
    data = merged_stack,
    mapping = aes(
      x = x,
      y = y,
      r = red,
      g = green,
      b = blue
    )
  ) +
  geom_sf(data = simulated_data) +
  coord_sf(crs = 4326)
} # }