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Create ggplot2 Raster Plots with RGB from 3 RasterLayers

Source: R/ggRGB.R
ggRGB.Rd

Calculates RGB color composite raster for plotting with ggplot2. Optional values for clipping and and stretching can be used to enhance the imagery.

Usage

ggRGB(
  img,
  r = 3,
  g = 2,
  b = 1,
  scale,
  maxpixels = 5e+05,
  stretch = "none",
  ext = NULL,
  limits = NULL,
  clipValues = "limits",
  quantiles = c(0.02, 0.98),
  ggObj = TRUE,
  ggLayer = FALSE,
  alpha = 1,
  coord_equal = TRUE,
  geom_raster = FALSE,
  nullValue = 0
)

Arguments

img

SpatRaster

r

Integer or character. Red layer in x. Can be set to NULL, in which case the red channel will be set to zero.

g

Integer or character. Green layer in x. Can be set to NULL, in which case the green channel will be set to zero.

b

Integer or character. Blue layer in x. Can be set to NULL, in which case the blue channel will be set to zero.

scale

Numeric. Maximum possible pixel value (optional). Defaults to 255 or to the maximum value of x if that is larger than 255

maxpixels

Integer. Maximal number of pixels used for plotting.

stretch

Character. Either 'none', 'lin', 'hist', 'sqrt' or 'log' for no stretch, linear, histogram, square-root or logarithmic stretch.

ext

Extent or SpatExtent object to crop the image

limits

Vector or matrix. Can be used to reduce the range of values. Either a vector of two values for all bands (c(min, max)) or a 3x2 matrix with min and max values (columns) for each layer (rows).

clipValues

Matrix, numeric vector, string or NA. Values to reset out of range (out of limits) values to. By default ('limits') values are reset to limits. A single value (e.g. NA) will be recycled to all lower/higher clippings, A vector of length two (c(min,max)) can be used to specify lower and higher replace values, applied to all bands. A two column matrix (typically with three rows) can be used to fully control lower and upper clipping values differently for each band.

quantiles

Numeric vector with two elements. Min and max quantiles to stretch. Defaults to 2% stretch, i.e. c(0.02,0.98).

ggObj

Logical. If TRUE a ggplot2 object is returned. If FALSE a data.frame with coordinates and color will be returned.

ggLayer

Logical. If TRUE a ggplot2 layer is returned. This is useful if you want to add it to an existing ggplot2 object. Note that if TRUE & annotate = FALSE you have to add a scale_fill_identity() manually in your call to ggplot().

alpha

Numeric. Transparency (0-1).

coord_equal

Logical. Force addition of coord_equal, i.e. aspect ratio of 1:1. Typically useful for remote sensing data (depending on your projection), hence it defaults to TRUE. Note howver, that this does not apply if (ggLayer=FALSE).

geom_raster

Logical. If FALSE annotation_raster is used, otherwise geom_raster()+scale_fill_identity is used. Note that you can't use scale_fill* in addition to the latter, because it already requires scale_fill_identity().

nullValue

Numeric. Intensity value used for NULL layers in color compositing. E.g. set g=NULL and fix green value at 0.5 (defaults to 0).

Value

ggObj = TRUE:ggplot2 plot
ggLayer = TRUE:ggplot2 layer to be combined with an existing ggplot2
ggObj = FALSE:data.frame in long format suitable for plotting with ggplot2, includes the pixel values and the calculated colors

Details

Functionality is based on plotRGB from the raster package.

See also

ggR, fortifySpatRaster

Examples

  
library(ggplot2)

ggRGB(rlogo, r=1, g=2, b=3)


## Define minMax ranges
ggRGB(rlogo, r=1,g=2, b=3, limits = matrix(c(100,150,10,200,50,255),  ncol = 2, by = TRUE))


## Perform stong linear contrast stretch
ggRGB(rlogo, r = 1, g = 2, b = 3,stretch = "lin", quantiles = c(0.2, 0.8))


## Use only two layers for color calculation
ggRGB(rlogo, r = 1, g = 2, b = NULL)


## Return only data.frame
df <- ggRGB(rlogo, ggObj = FALSE)
head(df)
#>     x    y      fill
#> 1 0.5 76.5 #FFFFFFFF
#> 2 1.5 76.5 #FFFFFFFF
#> 3 2.5 76.5 #FFFFFFFF
#> 4 3.5 76.5 #FFFFFFFF
#> 5 4.5 76.5 #FFFFFFFF
#> 6 5.5 76.5 #FFFFFFFF

## Use in layer-mode, e.g. to add to another plot
wave <- data.frame(x = c(0, 0:100,100), y = c(0,sin(seq(0,2*pi,pi/50))*10+20, 0))
p <- ggplot(wave, aes(x, y)) 
p + ggRGB(rlogo, ggLayer = TRUE) +
       geom_polygon(aes(x, y), fill = "blue", alpha = 0.4) +
       coord_equal(ylim=c(0,75))