Arrow Ornaments

Wings

The ‘wings’ ornament places two symmetric triangles on either side of the line, and can be called using the arrow_head_wings() function. The offset parameter determines at what angle the triangle departs from the line end. The inset parameter determines the angle inside the corner that is not on the line. If you ensure that inset + offset equals 90, you can mimic grid::arrow(..., type = "closed") (2nd example). The length_head arguments determines the distance between the red line at the arrow tip and the blue line, where the triangle re-joins the line.

Below you can get an impression what kinds of shapes you can make with the wings arrowhead.

Line

The ‘line’ ornament draws two line segments departing from the line end, and can be set using the arrow_head_line() function. The linewidth aesthetic determines the thickness of the departing line, in that the line width is the same between the path and the ornament. The size of the arrow is once again determined by the length_head argument, but now encompasses the length of the protruding lines instead of the reconnection point back on the path.

Minimal

The ‘minimal’ ornament isn’t truly an ornament, but determines how the arrow shaft gets notched. Therefore, it is independent of any length_head you might set, and is only dependent on the angle argument and the linewidth aesthetic.

Feather

The ‘feather’ ornament places two trapeziums on either side of the line, and can be called using the arrow_fins_feather() function. Contrary to many other ornaments, the feather ornament isn’t defined by any angle. It is instead defined by the ‘height’ of the trapezium and the distances along the path from the inner start and end points to the outer ones called ‘indent’ and ‘outdent’. The length_fins argument determines the total width of the trapezium.

Below are some examples of what different settings look like with this ornament.

Line

The ‘line’ fins ornament mirrors the ‘line’ head ornament: it draws two line segments departing from the line end and can be set using the arrow_fins_line() function. Again the linewidth aesthetic determines the thickness of the departing line, in that the line width is the same between the path and the ornament. This size of the arrow is determined by the length_fins argument, but in contrast to arrow_fins_line(), the length_fins argument applies to the inner edge. Also in contrast, the angle is measured from the extended path to the lines, rather than from the path itself.

Another notable difference is that in arrow_fins_line() the most extreme parts are at the path’s end and don’t protrude beyond. For comparison, take a look at the 5th example in arrow_head_line() and the first 4 examples below:

Minimal

The ‘minimal’ fin ornament again isn’t truly an ornament, but it determines how the arrow shaft gets notched. Like arrow_head_minimal(), arrow_fins_minimal() doesn’t depend on any length_fins you might set and only depends on the angle argument and the linewidth aesthetic. The only difference between arrow_head_minimal() and arrow_fins_minimal(), is what part is considered the angle.

Cups

Not more suitable for arrow head than for fins, the ‘cup’ ornament may fit both ends of a path. The cup shape can be specified using the arrow_cup() function and it follows a circular arc around the endpoint of a path at some distance given by the resect parameter. There are two ways these cups can be specified. The first one is by the angle or the arc, which can be given by using the arrow_cup(angle = ...) function. If the angle is left as NULL, the ornament looks for the length_{head/fins} and uses that as the arc-length to draw the arc, which is the second specification.

The cup shape can make it easier to single out some observations from the rest.

ggplot(mtcars, aes(disp, mpg)) +
  geom_point(aes(colour = factor(cyl))) +
  geom_arrow_curve(
    data = ~ subset(.x, rownames(.x) == "Hornet 4 Drive"),
    aes(xend = 300, yend = 25),
    arrow_fins = arrow_cup(angle = 360), resect_fins = 1.5
  ) +
  annotate(
    "text", x = 300, y = 25,
    label = "Hornet 4 Drive",
    vjust = -1
  )