Spatial line segments

While the implementation is slightly differrent, this function is intended to behave identically to ggplot2::geom_segment(). Use great_circle = FALSE and detail = NULL if you wish ignore the fact that the earth is round.

geom_spatial_segment(
  mapping = NULL,
  data = NULL,
  ...,
  crs = NULL,
  detail = waiver(),
  great_circle = TRUE,
  wrap_dateline = TRUE,
  arrow = NULL,
  lineend = "butt",
  linejoin = "round",
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

StatSpatialSegment

Format

An object of class StatSpatialSegment (inherits from StatSpatialRect, Stat, ggproto, gg) of length 3.

Arguments

mapping

An aesthetic mapping created with ggplot2::aes().

data

A data frame or other object, coerced to a data.frame by ggplot2::fortify().

...

Passed to the combined stat/geom as parameters or fixed aesthetics.

crs

The crs of the x and y aesthetics, or NULL to use default lon/lat crs (with a message).

detail

Passed to sf::st_segmentize(): the number of line segments per quadrant of the bounding box. Increase this number for a smoother projected bounding box.

great_circle

If TRUE, use lwgeom::st_geod_segmentize() to connect the (x, y) and (xend, yend) with the shortest possible great circle along the earth.

wrap_dateline

When using great_circle = TRUE, using wrap_dateline = TRUE splits the great circle along the dateline. You may want to pass FALSE here if using arrow and a projection that wraps the dateline.

arrow

An arrow specification as a call to grid::arrow().

lineend

See ggplot2::geom_segment().

linejoin

How corners should be joined

na.rm

Should missing aesthetic values be removed?

show.legend, inherit.aes

See ggplot2::layer().

Examples

library(ggplot2)

# visualize flights from
# Halifax -> Anchorage -> Berlin -> Halifax
cities <- data.frame(
  lon = c(-63.58595, 116.41214, 13.50, -149.75),
  lat = c(44.64862, 40.19063, 52.51, 61.20),
  city = c("Halifax", "Beijing", "Berlin", "Anchorage"),
  city_to = c("Anchorage", "Beijing", "Berlin", "Halifax")
)

cities$lon_end <- cities$lon[c(4, 3, 1, 2)]
cities$lat_end <- cities$lat[c(4, 3, 1, 2)]

p <- ggplot(cities, aes(lon, lat, xend = lon_end, yend = lat_end)) +
  geom_spatial_point(crs = 4326)

# by default, geom_spatial_segment() connects points
# using the shortest distance along the face of the earth
# wrapping at the date line
p +
  geom_spatial_segment(crs = 4326) +
  coord_sf(crs = 3857)
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE


# to let the projection handle the dateline,
# use `wrap_dateline = FALSE` (most useful for
# when using `arrow`)
p +
  geom_spatial_segment(
    wrap_dateline = FALSE,
    arrow = grid::arrow(),
    crs = 4326
  ) +
  coord_sf(crs = 3995)


# to ignore the roundness of the earth, use
# `great_circle = FALSE`
p +
  geom_spatial_segment(
    great_circle = FALSE,
    arrow = grid::arrow(),
    crs = 4326
  ) +
  coord_sf(crs = 3995)