With Christmas tomorrow we have decided to create an animated Christmas Tree using {ggplot2}, {sf} and {gganimate}.

First we need a tree. To do this we have used an {sf} polygon where we pass in the coordinates of the Christmas tree as a list matrix to st_polygon. We can then use geom_sf to add this layer onto a ggplot object.

library(ggplot2)
library(gganimate)
library(sf)

tree_coords =
 list(
 matrix(
 c(-4, 0,
 -2.22, 2,
 -3.5, 2,
 -1.5, 4,
 -2.5, 4,
 -0.8, 6,
 -1.5, 6,
 0, 8,
 1.5, 6,
 0.8, 6,
 2.5, 4,
 1.5, 4,
 3.5, 2,
 2.22, 2,
 4, 0,
 -4, 0),
 ncol=2, byrow=T
 )
 )

tree = st_polygon(tree_coords)

gg_tree = ggplot() +
 geom_sf(aes(), data=tree)

gg_tree

Okay, so now we have a tree shape. Now we need to make it a little more Christmassy by changing:

• The color using: fill = "forestgreen", color = "darkgreen"
• Adding the trunk: geom_rect(aes(xmin = -0.75, xmax = 0.75, ymin = -2, ymax = 0), fill = "saddlebrown", color = "sienna4")
• Add a star on the top: geom_point(aes(x = 0, y = 8), color = "gold", shape = 8, size = 7, stroke = 3)
• Remove the axis with: theme_void()
• Set the border: coord_sf(xlim = c(-6, 6), ylim = c(-4, 10))
• Add a Christmas message: annotate("text", x = 0, y = 9.5, label = "Merry Christmas \n From Jumping Rivers!", size = 6)

Now our tree looks like this:

gg_tree = ggplot() +
 geom_sf(aes(), data=tree, fill = "forestgreen", color = "darkgreen") +
 geom_rect(aes(xmin = -0.75, xmax = 0.75, ymin = -2, ymax = 0), fill = "saddlebrown", color = "sienna4") +
 geom_point(aes(x = 0, y = 8), color = "gold", shape = 8, size = 7, stroke = 3) +
 theme_void() +
 coord_sf(xlim = c(-6, 6), ylim = c(-4, 10)) +
 annotate("text", x = 0, y = 9.5, label = "Merry Christmas \n From Jumping Rivers!", size = 6)

gg_tree

Next we need to use {sf} again to make some lights for the tree then {gganimate} to make the lights flash.

Placing the points within the boundaries of the tree was a trickier task than we expected until we fell upon st_sample which we can pass a polygon to and it’ll create some sample points within the boundaries. We also create a vector to colour the points.

points = st_sample(tree, 75)
colours = sample(c("red", "yellow", "blue"), 75, replace = TRUE)

gg_tree = ggplot() +
 geom_sf(aes(), data=tree, fill = "forestgreen", color = "darkgreen") +
 geom_sf(aes(), data=points, color = colours) +
 geom_rect(aes(xmin = -0.75, xmax = 0.75, ymin = -2, ymax = 0), fill = "saddlebrown", color = "sienna4") +
 geom_point(aes(x = 0, y = 8), color = "gold", shape = 8, size = 7, stroke = 3) +
 theme_void() +
 coord_sf(xlim = c(-6, 6), ylim = c(-4, 10)) +
 annotate("text", x = 0, y = 9.5, label = "Merry Christmas \n From Jumping Rivers!", size = 6)

gg_tree

We can now animate it to make the lights sparkle using transition_time and ease_aes:

gg_tree +
 transition_time(1:75) +
 ease_aes('linear')

Lastly, have a great Christmas and New Year from the Jumping Rivers team!

For updates and revisions to this article, see the original post