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Wind rose glyphs: a map of local wind roses

geom_wind_rose.Rd

Draws a star glyph for each block of grid cells in a wind rose, showing the strength of flow toward each of the eight neighbors. stat_wind_rose() does the computation: converting conductance to flow, averaging over blocks, and building glyph polygons. geom_wind_rose() draws them, coloring each glyph by its net flow direction and graying it out where flow has little net direction.

Usage

geom_wind_rose(
  mapping = NULL,
  data = NULL,
  stat = StatWindRose,
  position = "identity",
  ...,
  res = 15,
  scale = 1,
  saturation = 0.5,
  center = TRUE,
  bearing_scale = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

stat_wind_rose(
  mapping = NULL,
  data = NULL,
  geom = GeomWindRose,
  position = "identity",
  ...,
  res = 15,
  scale = 1,
  saturation = 0.5,
  center = TRUE,
  bearing_scale = NULL,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Aesthetic mappings created by ggplot2::aes(). x and y (cell center coordinates, in degrees longitude and latitude) must be mapped, usually in the plot's main call: ggplot(rose, aes(x, y)). The eight conductance columns (SW, W, NW, N, NE, E, SE, S) are mapped automatically to columns of the same names, as produced by fortify() on a wind_rose (see fortify.windscape). If your columns are named differently, map them in this layer's mapping rather than in ggplot2::ggplot(): the automatic mappings are part of the layer, so they take precedence over plot-level ones.

data

A data frame, or a wind_rose, which is converted with fortify(). Default is to inherit the plot's data.

stat, geom

Use to override the default pairing of stat_wind_rose() and geom_wind_rose().

position

Position adjustment; see ggplot2::layer().

...

Other arguments passed to ggplot2::layer(), such as fixed aesthetics like color = "black".

res

Approximate number of glyphs along the longer side of the data's extent. Blocks of grid cells are sized to be approximately square in km. The same blocks are used in every panel, so faceted glyphs are directly comparable. Default 15.

scale

Multiplier for the size of all glyphs. At the default of 1, the longest ray of a typical large glyph (the 90th percentile across all glyphs in the layer, including all panels) is half the spacing between glyphs.

saturation

Consistency (see Computed variables) at and above which glyph fill is shown at full strength; glyphs with lower consistency are blended toward gray. Set to 0 to disable blending. Default 0.5.

center

Logical: draw a point at each glyph's center? Default TRUE.

bearing_scale

Logical: add scale_fill_bearing() to the plot? Default TRUE if fill is neither mapped nor set, otherwise FALSE.

na.rm, show.legend, inherit.aes

See ggplot2::layer().

Value

A ggplot2 layer (with bearing_scale = TRUE, a list of a layer and a scale).

Details

Each glyph's eight rays point toward the eight neighbors, with length proportional to flow in that direction: conductance times the distance to the neighbor, averaged over the block, in km/h. Unlike conductance, which is a rate per grid cell, flow does not depend on cell size, so it can be averaged across cells and compared across latitudes. The flows sum to the mean wind speed, and their vector sum is the net flow.

Glyphs are built in longitude/latitude coordinates, scaled so that their shapes are correct in km at each glyph's latitude. Use ggplot2::coord_quickmap() or ggplot2::coord_sf() with a longitude/latitude CRS so that the map's aspect ratio matches; in projected coordinates, glyph angles are distorted.

Computed variables

  • bearing: direction of net flow, in degrees clockwise from north.

  • consistency: net flow divided by total flow (mean resultant length); near 1 where wind blows predominantly one way, near 0 where it has no net direction.

  • speed: total flow, the mean wind speed in km/h (if trans = 1 in wind_rose() and wind speeds are in m/s).

  • net: net flow speed, in km/h.

  • n: number of grid cells in the glyph's block.

  • x0, y0: glyph center, the mean coordinates of the cells in its block.

By default, fill is mapped to after_stat(bearing) and the consistency aesthetic to after_stat(consistency).

Examples

library(ggplot2)
rose <- windscape_example("wind_rose")
ggplot(rose, aes(x, y)) +
  geom_wind_rose() +
  coord_quickmap()


# a background of mean wind speed: the glyphs use the fill scale, so show the background
# with alpha (or use a second fill scale, e.g. from the ggnewscale package)
ggplot(rose, aes(x, y)) +
  geom_raster(aes(alpha = speed), fill = "gray20") +
  geom_wind_rose() +
  coord_quickmap()


# faceting: glyphs use the same blocks and size scale in every panel
d <- rbind(cbind(fortify(rose), version = "original"),
           cbind(fortify(rose), version = "copy"))
ggplot(d, aes(x, y)) +
  geom_wind_rose(res = 10) +
  facet_wrap(~version) +
  coord_quickmap()