ggR: Plot RasterLayers in ggplot with greyscale

In bleutner/RStoolbox: Remote Sensing Data Analysis

Plot RasterLayers in ggplot with greyscale

Description

Plot single layer imagery in grey-scale. Can be used with a SpatRaster.

Usage

ggR(
  img,
  layer = 1,
  maxpixels = 5e+05,
  alpha = 1,
  hue = 1,
  sat = 0,
  stretch = "none",
  quantiles = c(0.02, 0.98),
  ext = NULL,
  coord_equal = TRUE,
  ggLayer = FALSE,
  ggObj = TRUE,
  geom_raster = FALSE,
  forceCat = FALSE
)

Arguments

img	SpatRaster
layer	Character or numeric. Layername or number. Can be more than one layer, in which case each layer is plotted in a subplot.
maxpixels	Integer. Maximal number of pixels to sample.
alpha	Numeric. Transparency (0-1).
hue	Numeric. Hue value for color calculation [0,1] (see hsv). Change if you need anything else than greyscale. Only effective if sat > 0.
sat	Numeric. Saturation value for color calculation [0,1] (see hsv). Change if you need anything else than greyscale.
stretch	Character. Either 'none', 'lin', 'hist', 'sqrt' or 'log' for no stretch, linear, histogram, square-root or logarithmic stretch.
quantiles	Numeric vector with two elements. Min and max quantiles to stretch to. Defaults to 2% stretch, i.e. c(0.02,0.98).
ext	Extent object to crop the image
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 however, that this does not apply if (ggLayer=FALSE).
ggLayer	Logical. Return only a ggplot layer which must be added to an existing ggplot. If FALSE s stand-alone ggplot will be returned.
ggObj	Logical. Return a stand-alone ggplot object (TRUE) or just the data.frame with values and colors
geom_raster	Logical. If FALSE uses annotation_raster (good to keep aestetic mappings free). If TRUE uses geom_raster (and aes(fill)). See Details.
forceCat	Logical. If TRUE the raster values will be forced to be categorical (will be converted to factor if needed).

Details

When img contains factor values and annotation=TRUE, the raster values will automatically be converted to numeric in order to proceed with the brightness calculation.

The geom_raster argument switches from the default use of annotation_raster to geom_raster. The difference between the two is that geom_raster performs a meaningful mapping from pixel values to fill colour, while annotation_raster is simply adding a picture to your plot. In practice this means that whenever you need a legend for your raster you should use geom_raster = TRUE. This also allows you to specify and modify the fill scale manually. The advantage of using annotation_raster (geom_raster = TRUE) is that you can still use the scale_fill* for another variable. For example you could add polygons and map a value to their fill colour. For more details on the theory behind aestetic mapping have a look at the ggplot2 manuals.

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

See Also

ggRGB, fortifySpatRaster

Examples

library(ggplot2)
library(terra)

## Simple grey scale annotation
ggR(rlogo)

## With linear stretch contrast enhancement
ggR(rlogo, stretch = "lin", quantiles = c(0.1,0.9))

## ggplot with geom_raster instead of annotation_raster
## and default scale_fill*
ggR(rlogo, geom_raster = TRUE)

## with different scale
ggR(rlogo, geom_raster = TRUE) +
        scale_fill_gradientn(name = "mojo", colours = rainbow(10)) +
        ggtitle("**Funkadelic**")

## Plot multiple layers

ggR(lsat, 1:6, geom_raster=TRUE, stretch = "lin") +
    scale_fill_gradientn(colors=grey.colors(100), guide = "none") +
    theme(axis.text = element_text(size=5),
          axis.text.y = element_text(angle=90),
          axis.title=element_blank())

## Don't plot, just return a data.frame
df <- ggR(rlogo, ggObj = FALSE)
head(df, n = 3)

## Layermode (ggLayer=TRUE)
data <- data.frame(x = c(0, 0:100,100), y = c(0,sin(seq(0,2*pi,pi/50))*10+20, 0))
ggplot(data, aes(x, y)) +  ggR(rlogo, geom_raster= FALSE, ggLayer = TRUE) +
       geom_polygon(aes(x, y), fill = "blue", alpha = 0.4) +
       coord_equal(ylim=c(0,75))

## Categorical data 
## In this case you probably want to use geom_raster=TRUE 
## in order to perform aestetic mapping (i.e. a meaningful legend)
rc   <- rlogo
rc[] <- cut(rlogo[[1]][], seq(0,300, 50))
ggR(rc, geom_raster = TRUE)

## Legend cusomization etc. ...
ggR(rc, geom_raster = TRUE) + scale_fill_continuous(labels=paste("Class", 1:6))

## Creating a nicely looking DEM with hillshade background
terr <- terrain(srtm, c("slope", "aspect"))
hill <- shade(terr[["slope"]], terr[["aspect"]])
ggR(hill)

ggR(hill) + 
   ggR(srtm, geom_raster = TRUE, ggLayer = TRUE, alpha = 0.3) +
   scale_fill_gradientn(colours = terrain.colors(100), name = "elevation")

bleutner/RStoolbox documentation built on Nov. 30, 2024, 9:47 p.m.