click_sample: Sample raster values within map categories

In AGAuffret/HistMapR: Rapid digitization of historical land-use maps in R

Sample raster values within map categories

Description

Function for sampling the RGB values at n points of an image within n categories, using the click() function from the raster package. These values can then be used to define thresholds for reclassifying the raster image.

Usage

click_sample(in.raster, cats = NULL, npoints = 10, print.values = FALSE, type = "p", plot.cols = TRUE, ...)

Arguments

in.raster	The SpatRaster to sample. Only works for an image file, and bands MUST be named "red", "green", and "blue" (exactly, in that order) for it to work.
cats	A vector of the names of land-use categories of interest (string).
npoints	The number of times to sample each category. More points means more representative results, but generally the default is enough if you make sure that you sample the full range of colours for each category, provided points are well chosen. Default = 10.
print.values	Logical. Print the RGB values of each point as you go. Default = FALSE.
type	Logical. From click. Do you want to plot the points on the image so you know where you've already clicked (and if you miss!). Default = TRUE.
plot.cols	Logical. Produce the plot of max or min colours once sampling is finished. Requires packages ggplot and gridExtra. Default = TRUE.
...	additional parameters passed to plot_colour_table

Value

Returns a list with three objects:

sample.table	Dataframe. The values for each point clicked and the category they were assigned in.
colour.summary	Dataframe. Summary of max, min and mean values for each colour band in each category
colour.plot	Plot. Visualises the values in colour.summary and check they fit expectations.

Author(s)

Alistair Auffret and Adam Kimberley

References

Auffret, A.G., Kimberley, A., et al., 2017, HistMapR: Rapid digitization of historical maps in R, Methods in Ecology and Evolution, doi: 10.1111/2041-210X.12788., Link. GitHub repository.

Hijmans, R.J. (2023) terra: Spatial Data Analysis. R package version 1.7-29, https://CRAN.R-project.org/package=terra.

Examples

	ras.loc <- system.file("data/ras.smoothed.tiff", package="HistMapR")
	ras.smoothed <- rast(ras.loc)
	click_sample(in.raster=ras.smoothed, cats = c("Arable", "Open", "Forest"), npoints = 3, print.values = FALSE, type = "p", plot.cols = TRUE)
	 

AGAuffret/HistMapR documentation built on Feb. 23, 2025, 1:11 a.m.