geom_vector: Vector Layers for ggplot2

In ggvfields: Vector Field Visualizations with 'ggplot2'

Vector Layers for ggplot2

Description

Create layers for drawing vectors on ggplot2 plots. These functions accept wide-format data with the required aesthetics x and y plus either xend and yend or one of the alternative specifications: fx and fy, or angle/ angle_deg and distance.

Usage

geom_vector(
  mapping = NULL,
  data = NULL,
  stat = StatVector,
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  center = TRUE,
  normalize = TRUE,
  tail_point = FALSE,
  eval_point = FALSE,
  L = NULL,
  arrow = grid::arrow(angle = 25, length = unit(0.025, "npc"), type = "closed")
)

stat_vector(
  mapping = NULL,
  data = NULL,
  geom = GeomStream,
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  center = TRUE,
  normalize = TRUE,
  tail_point = FALSE,
  eval_point = FALSE,
  L = NULL,
  arrow = grid::arrow(angle = 25, length = unit(0.025, "npc"), type = "closed")
)

geom_vector2(
  mapping = NULL,
  data = NULL,
  stat = StatVector,
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  center = FALSE,
  tail_point = TRUE,
  eval_point = FALSE,
  L = NULL,
  arrow = NULL
)

stat_vector2(
  mapping = NULL,
  data = NULL,
  geom = GeomStream,
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  center = FALSE,
  tail_point = TRUE,
  eval_point = FALSE,
  L = NULL,
  arrow = NULL
)

Arguments

mapping	A set of aesthetic mappings created by ggplot2::aes(). Required: Must include x and y; in addition, either xend and yend or one of the alternative specifications (fx/ fy or angle/ angle_deg and distance) must be provided.
data	A data frame containing the vector data in wide format.
stat	The statistical transformation to use on the data (default: StatVector).
position	Position adjustment, either as a string or the result of a position adjustment function.
...	Other arguments passed on to grid::layer().
na.rm	Logical. If FALSE (the default), missing values are removed with a warning.
show.legend	Logical. Should this layer be included in the legends?
inherit.aes	Logical. If FALSE, overrides the default aesthetics rather than combining with them.
center	Logical. If TRUE, the vector is recentered so that the original ⁠(x, y)⁠ becomes the midpoint (default is TRUE for geom_vector() and FALSE for geom_vector2()).
normalize	Logical. If TRUE, the vector endpoints are scaled to unit length before being scaled by L (default: TRUE).
tail_point	Logical. If TRUE, a point is drawn at the tail (the starting point) of each vector (default is FALSE for geom_vector() and TRUE for geom_vector2()).
eval_point	Logical. If TRUE, a point is drawn at the evaluation point corresponding to the original (untransformed) seed point before any centering or normalization (default: FALSE).
L	Numeric scalar. The desired length for the vectors in data units. If NULL (the default), a value is computed automatically based on the plot’s x and y limits.
arrow	An optional grid::arrow() specification to add arrowheads to the vectors (default: grid::arrow(angle = 25, length = unit(0.025, "npc"), type = "closed")).
geom	The geometric object used to render the streamline (only used in stat_stream(); defaults to GeomStream).

Details

When specifying the vector direction using polar coordinates, you can provide either:

• angle: the vector direction in radians.

• angle_deg: the vector direction in degrees (which is automatically converted to radians).

The endpoints are computed by translating the starting point using these polar coordinates along with the supplied distance.

The data is converted to long format (two rows per vector) via StatVector and rendered with GeomStream. Optionally, arrowheads can be added to indicate direction.

There are two variants:

• geom_vector(): Uses the user-supplied aesthetic mapping.

• geom_vector2(): Uses the same underlying stat (StatVector) but adds a default mapping for length = after_stat(norm), making the computed vector norm available as an aesthetic.

Value

A ggplot2 layer that can be added to a plot.

Aesthetics

geom_vector() and geom_vector2() understand the following aesthetics (required aesthetics are in bold):

• x

• y

• xend

• yend

• fx (alternative specification)

• fy (alternative specification)

• angle (vector direction in radians; alternative specification)

• angle_deg (vector direction in degrees; alternative specification, converted to radians)

• distance (with angle/angle_deg, used to compute endpoints)

• alpha

• color

• fill

• group

• linetype

• size

Computed Variables

These are calculated by the 'stat' part of layers and can be accessed with delayed evaluation.

norm

Calculated as the Euclidean distance between the starting point (x, y) and the computed endpoint (xend, yend). This value is used to normalize the vector length when the normalize parameter is set to TRUE.

Examples

set.seed(1234)
n <- 10

# Generate wind data in polar coordinates
data <- data.frame(
  x = rnorm(n),
  y = rnorm(n),
  dir = runif(n, -pi, pi), # angle in radians
  spd = rchisq(n, df = 2)  # speed
) |>
  transform(fx = spd * cos(dir), fy = spd * sin(dir))

# Using fx/fy to compute endpoints
ggplot(data, aes(x, y)) +
  geom_vector(aes(fx = fx, fy = fy))

# Using angle (in radians) and distance to compute endpoints
ggplot(data, aes(x, y)) +
  geom_vector(aes(angle = dir, distance = spd))

# Using angle_deg (in degrees) and distance to compute endpoints
vectors3 <- data.frame(
  x = c(0, 1, 2),
  y = c(0, 1, 2),
  angle_deg = c(0, 90, 45),
  angle = c(0, pi/2, pi/4),
  distance = c(3, 4, 5)
)
ggplot(vectors3, aes(x, y)) +
  geom_vector(aes(angle_deg = angle_deg, distance = distance))

# Basic usage with explicit start and end points:
vectors1 <- data.frame(
  x    = c(0, 1, 2),
  y    = c(0, 1, 2),
  xend = c(3, 1, 5),
  yend = c(0, 5, 6)
)
ggplot(vectors1, aes(x = x, y = y, xend = xend, yend = yend)) +
  geom_vector()

# Using center = TRUE to recenter vectors:
ggplot(vectors1, aes(x = x, y = y, xend = xend, yend = yend)) +
  geom_vector(center = TRUE)

# Using normalize = TRUE to adjust vectors to unit length:
ggplot(vectors3, aes(x = x, y = y, angle = angle, distance = distance)) +
  geom_vector(normalize = TRUE)

# Using geom_vector2, which adds a default mapping for `length`
ggplot(vectors1, aes(x = x, y = y, xend = xend, yend = yend)) +
  geom_vector2()

ggvfields documentation built on April 3, 2025, 9:04 p.m.