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cartesian coordinate system with polar grid lines

Source: R/coord_cartpolar.R
coord_cartpolar.Rd

A cartesian coordinate system overlayed with a polar grid. It is used together with summary_wind_2d() in ggpolarplot().

Usage

coord_cartpolar(
  limit = NA,
  expand = TRUE,
  clip = "on",
  bg = NULL,
  grid = c("background", "foreground")
)

Arguments

limit

limit for coordsystem (xlim(-limit, limit), ylim(-limit, limit))

expand

if TRUE

clip

clip panel (not sure if used)

bg

raster for background image

grid

draw the lines and labels of the polar grid in the foreground or background

Warning

This coordinate system bends some ggplot2 internals (eg. diverted x axis). It works for our scope, but the testing was surficial. And probably some things could easily break. Things that breaks this coord:

  • setting limits in x scale

Examples

library(ggplot2)

df <- tibble::tribble(
  ~wd, ~ws, ~facet,
  0, 5, 1,
  0, 2.5, 1,
  0, 9.5, 1,
  0, 4, 1,
  90, 4, 1,
  180, 4, 1,
  270, 4, 1,
  30, 8, 2,
  120, 8, 2,
  200, 8, 2,
  300, 8, 2
)

df <- dplyr::mutate(df,
  u = .data$ws * sin(2 * pi * .data$wd / 360),
  v = .data$ws * cos(2 * pi * .data$wd / 360)
)

p <-  ggplot(df, aes(x=u, y=v)) + geom_point()

p + coord_cartpolar()



# y scale is used for uv scaling (negative breaks are ignored)
p  + coord_cartpolar() +
  scale_y_continuous(
    limits = c(-10, 10),
    breaks = c(-5, 0, 1, 2.5, 7.5, 10),
    expand = c(0, 0, 0, 0)
  )


# alternative argument limit of coord_cartpolar can be used
p  + coord_cartpolar(limit = 5)
#> Warning: Removed 3 rows containing missing values or values outside the scale range
#> (`geom_point()`).


# a continuous x scale is used to control the breaks and labels
# for wd. Setting limits in this scale will cause problems
p  + coord_cartpolar() +
  scale_x_continuous(
    breaks = c(0, 45, 90, 180, 270),
    labels = c("Nord", "NE", "E", "S", "W")
  )



# theming: only major grid is draw
p + coord_cartpolar() +
  theme(
    "panel.grid.major.x" = element_line(color = "red", linewidth = 2, linetyp = "dashed"),
    "panel.grid.major.y" = element_line(color = "green", arrow = arrow()),
    "axis.text.x" = element_text(color = "violet", size = 14, face = "bold"),
    "axis.text.y" = element_text(color = "blue")
  )



# background map
bb <- bbox_lv95(2683141, 1249040, 500)
bg <- get_stadia_map(bb)
#> ℹ © Stadia Maps © Stamen Design © OpenMapTiles © OpenStreetMap contributors.

p + coord_cartpolar(bg = bg)


# faceting
p + coord_cartpolar(bg = bg) +
  facet_wrap(vars(facet))


# if plotting a raster layer, use grid = "foreground" to draw
# the polar grid over the raster. an expand of c(0, 0.5, 0, 0.5)
# can be used to compensated the added 0.5 from raster
raster <- expand.grid(u = -10:10, v = -10:10)
raster$z <- runif(nrow(raster))
ggplot(raster, aes(x=u, y=v, fill=z)) +
  coord_cartpolar(bg = bg, grid = "foreground") +
  geom_raster(alpha = 0.5) +
  scale_y_continuous(expand = c(0, 0.5, 0, 0.5))


# -Inf, Inf, -Inf, Inf from annotation_raster get mapped
# over the complete panel
ggplot(raster, aes(x=u, y=v, fill=z)) +
  coord_cartpolar(grid = "foreground") +
  annotation_raster(bg, -Inf, Inf, -Inf, Inf) +
  geom_raster(alpha = 0.5) +
  scale_y_continuous(expand = c(0, 0.5, 0, 0.5))