Is it possible to rasterize a ggplot in such way that the resulting raster object represents the ggp-CodePudding

Is it possible to rasterize a ggplot in such way that the resulting raster object represents the ggplot?

I have a following ggplot p:

If I convert it to a raster object and plot it again it looks like this:

This is how I create and rasterize the plot p:

library(ratser)
library(ggplot)

p<-ggplot(wind_data, aes(x = lon, y = lat))  
  geom_segment(aes(xend = lon   0.1, yend = lat   0.1),
               arrow = arrow(length = unit(0.1, "cm")), size = 0.25)   

p<-p  theme_void()   coord_cartesian(xlim = c(3.604383, 14.60482), ylim = c(47.07157 ,54.73807 ))   theme(panel.border = element_blank(), panel.grid.major = element_blank(),
                            panel.grid.minor = element_blank(), axis.line = element_line(colour = "black") )



ggsave(plot=p, "my_ggplot.tiff", device = "tiff")
raster <- raster::raster("my_ggplot.tiff") # OR stack("my_ggplot.tiff") for colored images
lat_long <- ggplot_build(p)$layout$panel_params[[1]][c("x.range","y.range")]

extent(raster) <- c(lat_long$x.range,lat_long$y.range)
projection(raster) <- CRS(" proj=longlat  datum=WGS84")

Here is wind_data data.frame:

      wind_data<-structure(list(lon = c(8.87312091729266, 8.71871388830953, 10.5679127453358, 
10.7216122406487, 10.4141464047873, 10.5679127453358, 10.1064188710028, 
11.3357135330171, 11.4890576651767, 11.1822955254471), lat = c(54.6482360923283, 
54.5584019137964, 54.2888913181823, 54.2888913181823, 54.1990517614177, 
54.1990517614177, 54.0193686018903, 53.6599860593553, 53.6599860593553, 
53.5701370357575), dd = c(241, 238, 247, 240, 240, 246, 247, 
246, 245, 247)), class = "data.frame", row.names = c(NA, -10L
))

Here is the data of the plot p:

        p<-structure(list(data = structure(list(lon = c(8.87312091729266, 
8.71871388830953, 10.5679127453358, 10.7216122406487, 10.4141464047873, 
10.5679127453358, 10.1064188710028, 11.3357135330171, 11.4890576651767, 
11.1822955254471), lat = c(54.6482360923283, 54.5584019137964, 
54.2888913181823, 54.2888913181823, 54.1990517614177, 54.1990517614177, 
54.0193686018903, 53.6599860593553, 53.6599860593553, 53.5701370357575
), dd = c(241, 238, 247, 240, 240, 246, 247, 246, 245, 247)), class = "data.frame", row.names = c(NA, 
-10L)), layers = list(<environment>), scales = <environment>, 
    mapping = structure(list(x = ~lon, y = ~lat), class = "uneval"), 
    theme = structure(list(line = structure(list(), class = c("element_blank", 
    "element")), rect = structure(list(), class = c("element_blank", 
    "element")), text = structure(list(family = "", face = "plain", 
        colour = "black", size = 11, hjust = 0.5, vjust = 0.5, 
        angle = 0, lineheight = 0.9, margin = structure(c(0, 
        0, 0, 0), unit = 8L, class = c("margin", "simpleUnit", 
        "unit", "unit_v2")), debug = FALSE, inherit.blank = TRUE), class = c("element_text", 
    "element")), title = NULL, aspect.ratio = NULL, axis.title = structure(list(), class = c("element_blank", 
    "element")), axis.title.x = NULL, axis.title.x.top = NULL, 
        axis.title.x.bottom = NULL, axis.title.y = NULL, axis.title.y.left = NULL, 
        axis.title.y.right = NULL, axis.text = structure(list(), class = c("element_blank", 
        "element")), axis.text.x = NULL, axis.text.x.top = NULL, 
        axis.text.x.bottom = NULL, axis.text.y = NULL, axis.text.y.left = NULL, 
        axis.text.y.right = NULL, axis.ticks = NULL, axis.ticks.x = NULL, 
        axis.ticks.x.top = NULL, axis.ticks.x.bottom = NULL, 
        axis.ticks.y = NULL, axis.ticks.y.left = NULL, axis.ticks.y.right = NULL, 
        axis.ticks.length = structure(0, unit = 8L, class = c("simpleUnit", 
        "unit", "unit_v2")), axis.ticks.length.x = NULL, axis.ticks.length.x.top = NULL, 
        axis.ticks.length.x.bottom = NULL, axis.ticks.length.y = NULL, 
        axis.ticks.length.y.left = NULL, axis.ticks.length.y.right = NULL, 
        axis.line = structure(list(colour = "black", size = NULL, 
            linetype = NULL, lineend = NULL, arrow = FALSE, inherit.blank = FALSE), class = c("element_line", 
        "element")), axis.line.x = NULL, axis.line.x.top = NULL, 
        axis.line.x.bottom = NULL, axis.line.y = NULL, axis.line.y.left = NULL, 
        axis.line.y.right = NULL, legend.background = NULL, legend.margin = NULL, 
        legend.spacing = NULL, legend.spacing.x = NULL, legend.spacing.y = NULL, 
        legend.key = NULL, legend.key.size = structure(1.2, unit = 3L, class = c("simpleUnit", 
        "unit", "unit_v2")), legend.key.height = NULL, legend.key.width = NULL, 
        legend.text = structure(list(family = NULL, face = NULL, 
            colour = NULL, size = structure(0.8, class = "rel"), 
            hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL, 
            margin = NULL, debug = NULL, inherit.blank = TRUE), class = c("element_text", 
        "element")), legend.text.align = NULL, legend.title = structure(list(
            family = NULL, face = NULL, colour = NULL, size = NULL, 
            hjust = 0, vjust = NULL, angle = NULL, lineheight = NULL, 
            margin = NULL, debug = NULL, inherit.blank = TRUE), class = c("element_text", 
        "element")), legend.title.align = NULL, legend.position = "right", 
        legend.direction = NULL, legend.justification = NULL, 
        legend.box = NULL, legend.box.just = NULL, legend.box.margin = NULL, 
        legend.box.background = NULL, legend.box.spacing = NULL, 
        panel.background = NULL, panel.border = structure(list(), class = c("element_blank", 
        "element")), panel.spacing = structure(5.5, unit = 8L, class = c("simpleUnit", 
        "unit", "unit_v2")), panel.spacing.x = NULL, panel.spacing.y = NULL, 
        panel.grid = NULL, panel.grid.major = structure(list(), class = c("element_blank", 
        "element")), panel.grid.minor = structure(list(), class = c("element_blank", 
        "element")), panel.grid.major.x = NULL, panel.grid.major.y = NULL, 
        panel.grid.minor.x = NULL, panel.grid.minor.y = NULL, 
        panel.ontop = FALSE, plot.background = NULL, plot.title = structure(list(
            family = NULL, face = NULL, colour = NULL, size = structure(1.2, class = "rel"), 
            hjust = 0, vjust = 1, angle = NULL, lineheight = NULL, 
            margin = structure(c(5.5, 0, 0, 0), unit = 8L, class = c("margin", 
            "simpleUnit", "unit", "unit_v2")), debug = NULL, 
            inherit.blank = TRUE), class = c("element_text", 
        "element")), plot.title.position = "panel", plot.subtitle = structure(list(
            family = NULL, face = NULL, colour = NULL, size = NULL, 
            hjust = 0, vjust = 1, angle = NULL, lineheight = NULL, 
            margin = structure(c(5.5, 0, 0, 0), unit = 8L, class = c("margin", 
            "simpleUnit", "unit", "unit_v2")), debug = NULL, 
            inherit.blank = TRUE), class = c("element_text", 
        "element")), plot.caption = structure(list(family = NULL, 
            face = NULL, colour = NULL, size = structure(0.8, class = "rel"), 
            hjust = 1, vjust = 1, angle = NULL, lineheight = NULL, 
            margin = structure(c(5.5, 0, 0, 0), unit = 8L, class = c("margin", 
            "simpleUnit", "unit", "unit_v2")), debug = NULL, 
            inherit.blank = TRUE), class = c("element_text", 
        "element")), plot.caption.position = "panel", plot.tag = structure(list(
            family = NULL, face = NULL, colour = NULL, size = structure(1.2, class = "rel"), 
            hjust = 0.5, vjust = 0.5, angle = NULL, lineheight = NULL, 
            margin = NULL, debug = NULL, inherit.blank = TRUE), class = c("element_text", 
        "element")), plot.tag.position = "topleft", plot.margin = structure(c(0, 
        0, 0, 0), unit = 3L, class = c("simpleUnit", "unit", 
        "unit_v2")), strip.background = NULL, strip.background.x = NULL, 
        strip.background.y = NULL, strip.placement = NULL, strip.text = structure(list(
            family = NULL, face = NULL, colour = NULL, size = structure(0.8, class = "rel"), 
            hjust = NULL, vjust = NULL, angle = NULL, lineheight = NULL, 
            margin = NULL, debug = NULL, inherit.blank = TRUE), class = c("element_text", 
        "element")), strip.text.x = NULL, strip.text.y = NULL, 
        strip.switch.pad.grid = structure(2.75, unit = 8L, class = c("simpleUnit", 
        "unit", "unit_v2")), strip.switch.pad.wrap = structure(2.75, unit = 8L, class = c("simpleUnit", 
        "unit", "unit_v2"))), class = c("theme", "gg"), complete = TRUE, validate = TRUE), 
    coordinates = <environment>, facet = <environment>, plot_env = <environment>, 
    labels = list(x = "lon", y = "lat", xend = "lon   0.1", yend = "lat   0.1")), class = c("gg", 
"ggplot"))

If i understand it correctly the resulting raster object should have only min value 0 and max value 1 and represent the arrows in lat long coordinates. But it does not look like this. What am I doing wrong?

CodePudding user response：

Still not sure about this conversion on a meta level, but technically you should be able to solve it this way:

library(terra)
#> terra 1.6.33
library(geodata)

# write your plot to disk
ggsave(plot = p, "my_ggplot.jpeg")

# import as SpatRaster object
r <- rast("my_ggplot.jpeg")
#> Warning: [rast] unknown extent

# your object has 3 layers with values ranging from 0 to 255
r
#> class       : SpatRaster 
#> dimensions  : 1668, 3609, 3  (nrow, ncol, nlyr)
#> resolution  : 1, 1  (x, y)
#> extent      : 0, 3609, 0, 1668  (xmin, xmax, ymin, ymax)
#> coord. ref. :  
#> source      : my_ggplot.jpeg 
#> colors RGB  : 1, 2, 3 
#> names       : my_ggplot_1, my_ggplot_2, my_ggplot_3

summary(r)
#> Warning: [summary] used a sample
#>   my_ggplot_1   my_ggplot_2   my_ggplot_3 
#>  Min.   : 62   Min.   : 62   Min.   : 62  
#>  1st Qu.:255   1st Qu.:255   1st Qu.:255  
#>  Median :255   Median :255   Median :255  
#>  Mean   :254   Mean   :254   Mean   :254  
#>  3rd Qu.:255   3rd Qu.:255   3rd Qu.:255  
#>  Max.   :255   Max.   :255   Max.   :255

# provide proper georeferencing information by crs and extent definition
crs(r) <- " proj=longlat  datum=WGS84  no_defs  type=crs"
ext(r) <- c(3.604383, 14.60482, 47.07157, 54.73807) |> ext()
r
#> class       : SpatRaster 
#> dimensions  : 1668, 3609, 3  (nrow, ncol, nlyr)
#> resolution  : 0.003048057, 0.004596223  (x, y)
#> extent      : 3.604383, 14.60482, 47.07157, 54.73807  (xmin, xmax, ymin, ymax)
#> coord. ref. :  proj=longlat  datum=WGS84  no_defs 
#> source      : my_ggplot.jpeg 
#> colors RGB  : 1, 2, 3 
#> names       : my_ggplot_1, my_ggplot_2, my_ggplot_3

# this is optional, just to verify the correct position
adm <- geodata::gadm("de", path = tempdir())

# inspect result
plot(r)
plot(adm, add = TRUE, border = "red")