sf: Create GeoPDF using ggplot2 output object

Question

I try to use a map created in ggplot to save as *pdf in order to create a georeferencing pdf using the function sf::st_write() without success. In my example:

#Packages
library(ggplot2)
library(ggspatial)
library(sf)

# Get data set - x any are the points
all.stands.predict<-read.csv("https://raw.githubusercontent.com/Leprechault/trash/main/prediction__bug_2021-03-18.csv")
all.stands.predict<-all.stands.predict[all.stands.predict[,3]=="VILA PALMA",] # Area selection

#Create a map
(sites <- st_as_sf(all.stands.predict, coords = c("x", "y"), 
                   crs = 4326, agr = "constant"))
gg <- ggplot() +
  geom_sf(data=sites, color="red") +
  annotation_north_arrow(location = "bl", which_north = "true", 
                         pad_x = unit(0.3, "in"), pad_y = unit(0.5, "in"),
                         style = north_arrow_fancy_orienteering) + #Add a north arrow
  annotation_scale(location = "bl", width_hint = 0.55) + #Add a scale bar
  xlab("Longitude") + ylab("Latitude") +
  theme_bw() 

# I inspected the map created
plot(gg)

#Save map as GeoPDF 
st_write(gg, "mymap.pdf", driver = "pdf")

Obvisioly the output is:

Error in UseMethod("st_as_sf") : 
method not applicable for 'st_as_sf' applied to a class object "c('gg', 'ggplot')"

Any many ways to convert the ggplot object to a sf object doesn't work too. I not try yet the use of the packages like RQGIS or RSAGA.

Please, there is some approach for creating easily GeoPDF maps using sf?

user_2977164 · Answer

There are two steps in the solution. First, you convert ggplot2 object in raster and second convert the raster created (myGeoTiffgg.tif) to geoPDF (myGeoTiffgg.pdf) using gdal_translate in gdalUtils package.

# Save the plot
ggsave(plot=gg, "gg.tiff", device = "tiff", dpi = 600)

# Create a StackedRaster object from the saved plot
stackedRaster <- stack("gg.tiff")

# Get the GeoSpatial Components
lat_long <- ggplot_build(gg)$layout$panel_params[[1]][c("x_range","y_range")] 

# Supply GeoSpatial  data to the StackedRaster 
extent(stackedRaster) <- c(lat_long$x_range,lat_long$y_range)
projection(stackedRaster) <- CRS("+proj=longlat +datum=WGS84")

# Create the GeoTiff
writeRaster(stackedRaster, "myGeoTiffgg.tif", options="PHOTOMETRIC=RGB", datatype="INT1U",overwrite=TRUE)

#Save raster as GeoPDF
gdalUtils::gdal_translate("myGeoTiffgg.tif","myGeoTiffgg.pdf",of="PDF", ot="Byte",
               co="TILED=YES",verbose=TRUE, overwrite=T, a_srs="+proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0")
}
#

sf: Create GeoPDF using ggplot2 output object

1 Answers