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Function to plot percentiles by wind direction

Source: R/percentileRose.R
percentileRose.Rd

percentileRose() plots percentiles by wind direction with flexible conditioning. The plot can display multiple percentile lines or filled areas.

Usage

percentileRose(
  mydata,
  pollutant = "nox",
  wd = "wd",
  type = "default",
  percentile = c(25, 50, 75, 90, 95),
  smooth = FALSE,
  method = "default",
  cols = "default",
  angle = 10,
  mean = TRUE,
  mean.lty = 1,
  mean.lwd = 3,
  mean.col = "grey",
  fill = TRUE,
  intervals = NULL,
  angle.scale = 45,
  offset = 0,
  auto.text = TRUE,
  key.title = NULL,
  key.position = "bottom",
  strip.position = "top",
  plot = TRUE,
  key = NULL,
  ...
)

Arguments

mydata

A data frame minimally containing wd and a numeric field to plot — pollutant.

pollutant

Mandatory. A pollutant name corresponding to a variable in a data frame should be supplied e.g. pollutant = "nox". More than one pollutant can be supplied e.g. pollutant = c("no2", "o3") provided there is only one type.

wd

Name of wind direction field.

type

Character string(s) defining how data should be split/conditioned before plotting. "default" produces a single panel using the entire dataset. Any other options will split the plot into different panels - a roughly square grid of panels if one type is given, or a 2D matrix of panels if two types are given. type is always passed to cutData(), and can therefore be any of:

  • A built-in type defined in cutData() (e.g., "season", "year", "weekday", etc.). For example, type = "season" will split the plot into four panels, one for each season.

  • The name of a numeric column in mydata, which will be split into n.levels quantiles (defaulting to 4).

  • The name of a character or factor column in mydata, which will be used as-is. Commonly this could be a variable like "site" to ensure data from different monitoring sites are handled and presented separately. It could equally be any arbitrary column created by the user (e.g., whether a nearby possible pollutant source is active or not).

Most openair plotting functions can take two type arguments. If two are given, the first is used for the columns and the second for the rows.

percentile

The percentile value(s) to plot. Must be between 0–100. If percentile = NA then only a mean line will be shown.

smooth

Should the wind direction data be smoothed using a cyclic spline?

method

When method = "default" the supplied percentiles by wind direction are calculated. When method = "cpf" the conditional probability function (CPF) is plotted and a single (usually high) percentile level is supplied. The CPF is defined as CPF = my/ny, where my is the number of samples in the wind sector y with mixing ratios greater than the overall percentile concentration, and ny is the total number of samples in the same wind sector (see Ashbaugh et al., 1985).

cols

Colours to use for plotting. Can be a pre-set palette (e.g., "turbo", "viridis", "tol", "Dark2", etc.) or a user-defined vector of R colours (e.g., c("yellow", "green", "blue", "black") - see colours() for a full list) or hex-codes (e.g., c("#30123B", "#9CF649", "#7A0403")). Alternatively, can be a list of arguments to control the colour palette more closely (e.g., palette, direction, alpha, etc.). See openColours() and colourOpts() for more details.

angle

Default angle of “spokes” is when smooth = FALSE.

mean

Show the mean by wind direction as a line?

mean.lty

Line type for mean line.

mean.lwd

Line width for mean line.

mean.col

Line colour for mean line.

fill

Should the percentile intervals be filled (default) or should lines be drawn (fill = FALSE).

intervals

User-supplied intervals for the scale e.g. intervals = c(0, 10, 30, 50).

angle.scale

In radial plots (e.g., polarPlot()), the radial scale is drawn directly on the plot itself. While suitable defaults have been chosen, sometimes the placement of the scale may interfere with an interesting feature. angle.scale can take any value between 0 and 360 to place the scale at a different angle, or FALSE to move it to the side of the plots.

offset

offset controls the size of the 'hole' in the middle and is expressed on a scale of 0 to 100, where 0 is no hole and 100 is a hole that takes up the entire plotting area.

auto.text

Either TRUE (default) or FALSE. If TRUE titles and axis labels will automatically try and format pollutant names and units properly, e.g., by subscripting the "2" in "NO2". Passed to quickText().

key.title

Used to set the title of the legend. The legend title is passed to quickText() if auto.text = TRUE.

key.position

Location where the legend is to be placed. Allowed arguments include "top", "right", "bottom", "left" and "none", the last of which removes the legend entirely.

strip.position

Location where the facet 'strips' are located when using type. When one type is provided, can be one of "left", "right", "bottom" or "top". When two types are provided, this argument defines whether the strips are "switched" and can take either "x", "y", or "both". For example, "x" will switch the 'top' strip locations to the bottom of the plot.

plot

When openair plots are created they are automatically printed to the active graphics device. plot = FALSE deactivates this behaviour. This may be useful when the plot data is of more interest, or the plot is required to appear later (e.g., later in a Quarto document, or to be saved to a file).

key

Deprecated; please use key.position. If FALSE, sets key.position to "none".

...

Addition options are passed on to cutData() for type handling. Some additional arguments are also available, varying somewhat in different plotting functions:

  • title, subtitle, caption, tag, xlab and ylab control the plot title, subtitle, caption, tag, x-axis label and y-axis label. All of these are passed through to quickText() if auto.text = TRUE.

  • xlim, ylim and limits control the limits of the x-axis, y-axis and colorbar scales.

  • ncol and nrow set the number of columns and rows in a faceted plot.

  • fontsize overrides the overall font size of the plot by setting the text argument of ggplot2::theme(). It may also be applied proportionately to any openair annotations (e.g., N/E/S/W labels on polar coordinate plots).

  • Various graphical parameters are also supported: linewidth, linetype, shape, size, border, and alpha. Not all parameters apply to all plots. These can take a single value, or a vector of multiple values - e.g., shape = c(1, 2) - which will be recycled to the length of values needed.

  • lineend, linejoin and linemitre tweak the appearance of line plots; see ggplot2::geom_line() for more information.

  • In polar coordinate plots, annotate = FALSE will remove the N/E/S/W labels and any other annotations.

Value

an openair object

Details

percentileRose() calculates percentile levels of a pollutant and plots them by wind direction. One or more percentile levels can be calculated and these are displayed as either filled areas or as lines.

The wind directions are rounded to the nearest 10 degrees, consistent with surface data from the UK Met Office before a smooth is fitted. The levels by wind direction are optionally calculated using a cyclic smooth cubic spline using the option smooth. If smooth = FALSE then the data are shown in 10 degree sectors.

The percentileRose function compliments other similar functions including windRose(), pollutionRose(), polarFreq() or polarPlot(). It is most useful for showing the distribution of concentrations by wind direction and often can reveal different sources e.g. those that only affect high percentile concentrations such as a chimney stack.

Similar to other functions, flexible conditioning is available through the type option. It is easy for example to consider multiple percentile values for a pollutant by season, year and so on. See examples below.

percentileRose also offers great flexibility with the scale used and the user has fine control over both the range, interval and colour.

References

Ashbaugh, L.L., Malm, W.C., Sadeh, W.Z., 1985. A residence time probability analysis of sulfur concentrations at ground canyon national park. Atmospheric Environment 19 (8), 1263-1270.

See also

Other polar directional analysis functions: polarAnnulus(), polarCluster(), polarDiff(), polarFreq(), polarPlot(), pollutionRose(), windRose()

Author

David Carslaw

Jack Davison

Examples

# basic percentile plot
percentileRose(mydata, pollutant = "o3")


# 50/95th percentiles of ozone, with different colours
percentileRose(mydata, pollutant = "o3", percentile = c(50, 95), col = "brewer1")


if (FALSE) { # \dontrun{
# percentiles of ozone by year, with different colours
percentileRose(
  mydata,
  type = "year",
  pollutant = "o3",
  col = "brewer1",
  ncol = 4,
  nrow = 2
)

# percentile concentrations by season and day/nighttime..
percentileRose(
  mydata,
  type = c("daylight", "season"),
  pollutant = "o3",
  col = "brewer1"
)
} # }