R: Automatically create ggplots visualization from multiple rasters - r

Question

building my path in R, So I am still very bad especially in running loops and complexes functions...
What I am interested about is to automatically read a series of rasters in a particular folder and generate a simple ggplot visualization out of it (for each one of the rasters). Possibly exporting it to some folder would be also nice.
The further idea would be to overlap these visualizations and create an animated GIF, but this I can perhaps do outside of R... Just creating the maps would already be really nice...
With this I can load all rasters in my R enviroment:
myfiles = list.files(pattern = "*.asc")
for (i in 1:length(myfiles)) assign(myfiles[i], raster::raster(myfiles[i]))
While the basic ggplot code to build one of the map would be:
#Loading an example raster
hflow = raster::raster("D:/R.avaflow_graphs/Erla_E1_F01_results/Erla_E1_F01_ascii/Erla_E1_F01_hflow0000.asc")
hflow_spdf <- as(hflow, "SpatialPixelsDataFrame") # Creating a spdf
hflow_df <- as.data.frame(hflow_spdf) # Creating a df
colnames(hflow_df) <- c("value", "x", "y") # Assign x,y,values
ggplot() + # plotting the map
geom_tile(data=hflow_df, aes(x=x, y=y, fill=value), alpha=0.8) +
coord_equal()
For inspiration, I've been checking these 3 links, but still couldn't make it happen...
R apply raster function to a list of characters
https://gis.stackexchange.com/questions/377444/plotting-a-raster-stack-with-ggplot2
https://www.r-bloggers.com/2020/07/writing-functions-to-automate-repetitive-plotting-tasks-in-ggplot2/
Thanks beforehand!
PL

Answer 1

The first part can be easily done with a simple sapply to create a plot for each image and save it to disk using ggsave. The gif creation can also be done inside R using the magick package. You just need to read the exported plots as images, then perform a join, animate and export as gif. Here's the code to perform the complete procedure.
library(magick)
library(ggplot2)
# List all raster files
myfiles = list.files(pattern = "*.asc")
# Loop to create plots for each image
sapply(myfiles, function(x){
# Get image names
im_name <- gsub("\\.[A-z]+$", "", x)
# Load image as raster
im <- raster::raster(x)
# Transform to df
hflow_spdf <- as(im, "SpatialPixelsDataFrame") # Creating a spdf
hflow_df <- as.data.frame(hflow_spdf) # Creating a df
colnames(hflow_df) <- c("value", "x", "y") # Assign x,y,values
# Make plot
ggplot() + # plotting the map
geom_tile(data=hflow_df, aes(x=x, y=y, fill=value), alpha=0.8) +
# Added fill_distiller to define filling palette
scale_fill_distiller(type = "seq",
palette = "Greys") +
coord_equal()
# Save plot
ggsave(paste0(im_name, ".png"),
device = "png",
width = 10,
height = 10,
units = "cm",
dpi = 150)
})
# Create gif
# List plots files
plots <- list.files(pattern = ".png")
# Read the plots as image
plots_list <- lapply(plots, image_read)
# Join the list of plots
plot_joined <- image_join(plots_list)
# Create animation, defining the frames per second (fps)
plot_animated <- image_animate(plot_joined, fps = 1)
# Write animation as gif
image_write(image = plot_animated,
path = "plots_anim.gif")