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Add heading endpoint markers on the unit circle

Source: R/circular_plotting.R
add_heading_points.Rd

Draws a hollow circle at `(cos(heading), sin(heading))` for each row of a headings data frame, placing one marker per trajectory on the unit-circle boundary at the derived heading direction. The data frame is normally the output of [derive_headings()].

Usage

add_heading_points(
  headings_df,
  colour_col = NULL,
  colour = NULL,
  size = 2,
  alpha = 1
)

Arguments

headings_df

Data frame with a `heading` column (angles in radians).

colour_col

Name of a column in `headings_df` to map to the colour aesthetic. When `NULL` (default), the value of `attr(headings_df, "colour_col")` is used if set – so heading markers automatically inherit the colour mapping from the associated trajectory plot when that attribute is present. Ignored when `colour` is supplied.

colour

Fixed colour string. Overrides `colour_col` when supplied; when `NULL` and no `colour_col` resolves, defaults to `"black"`.

size

Point size passed to `geom_point`.

alpha

Point alpha transparency.

Value

A `geom_point()` layer (shape = 1, hollow circle).

See also

[add_heading_vectors()], [derive_headings()]

Examples

library(ggplot2)
# headings from a TrajSet via derive_headings(ts, rule = "crossing", ...)
hd <- data.frame(id = "A", time = 1, heading = pi / 4)
ggplot() + coord_fixed() + add_heading_points(hd)

ggplot() + coord_fixed() + add_heading_points(hd, colour = "steelblue")