Trajectory line plots with conditioning

This function plots back trajectories. This function requires that data are imported using the importTraj function.

Usage

trajPlot(
  mydata,
  lon = "lon",
  lat = "lat",
  pollutant = "height",
  type = "default",
  map = TRUE,
  group = NA,
  map.fill = TRUE,
  map.res = "default",
  map.cols = "grey40",
  map.border = "black",
  map.alpha = 0.4,
  map.lwd = 1,
  map.lty = 1,
  projection = "lambert",
  parameters = c(51, 51),
  orientation = c(90, 0, 0),
  grid.col = "deepskyblue",
  grid.nx = 9,
  grid.ny = grid.nx,
  npoints = 12,
  origin = TRUE,
  plot = TRUE,
  ...
)

Arguments

mydata

Data frame, the result of importing a trajectory file using importTraj.

lon

Column containing the longitude, as a decimal.

lat

Column containing the latitude, as a decimal.

pollutant

Pollutant to be plotted. By default the trajectory height is used.

type

type determines how the data are split, i.e., conditioned, and then plotted. The default is will produce a single plot using the entire data. Type can be one of the built-in types as detailed in cutData e.g. "season", "year", "weekday" and so on. For example, type = "season" will produce four plots — one for each season.

It is also possible to choose type as another variable in the data frame. If that variable is numeric, then the data will be split into four quantiles (if possible) and labelled accordingly. If type is an existing character or factor variable, then those categories/levels will be used directly. This offers great flexibility for understanding the variation of different variables and how they depend on one another.

type can be up length two e.g. type = c("season", "weekday") will produce a 2x2 plot split by season and day of the week. Note, when two types are provided the first forms the columns and the second the rows.

map

Should a base map be drawn? If TRUE the world base map from the maps package is used.

group

It is sometimes useful to group and colour trajectories according to a grouping variable. See example below.

map.fill

Should the base map be a filled polygon? Default is to fill countries.

map.res

The resolution of the base map. By default the function uses the ‘world’ map from the maps package. If map.res = "hires" then the (much) more detailed base map ‘worldHires’ from the mapdata package is used. Use library(mapdata). Also available is a map showing the US states. In this case map.res = "state" should be used.

map.cols

If map.fill = TRUE map.cols controls the fill colour. Examples include map.fill = "grey40" and map.fill = openColours("default", 10). The latter colours the countries and can help differentiate them.

map.border

The colour to use for the map outlines/borders. Defaults to "black".

map.alpha

The transparency level of the filled map which takes values from 0 (full transparency) to 1 (full opacity). Setting it below 1 can help view trajectories, trajectory surfaces etc. and a filled base map.

map.lwd

The map line width, a positive number, defaulting to 1.

map.lty

The map line type. Line types can either be specified as an integer (0 = blank, 1 = solid (default), 2 = dashed, 3 = dotted, 4 = dotdash, 5 = longdash, 6 = twodash) or as one of the character strings "blank", "solid", "dashed", "dotted", "dotdash", "longdash", or "twodash", where "blank" uses 'invisible lines' (i.e., does not draw them).

projection

The map projection to be used. Different map projections are possible through the mapproj package. See ?mapproject for extensive details and information on setting other parameters and orientation (see below).

parameters

From the mapproj package. Optional numeric vector of parameters for use with the projection argument. This argument is optional only in the sense that certain projections do not require additional parameters. If a projection does not require additional parameters then set to null i.e. parameters = NULL.

orientation

From the mapproj package. An optional vector c(latitude, longitude, rotation) which describes where the "North Pole" should be when computing the projection. Normally this is c(90, 0), which is appropriate for cylindrical and conic projections. For a planar projection, you should set it to the desired point of tangency. The third value is a clockwise rotation (in degrees), which defaults to the midrange of the longitude coordinates in the map.

grid.col

The colour of the map grid to be used. To remove the grid set grid.col = "transparent".

grid.nx, grid.ny

The approximate number of ticks to draw on the map grid. grid.nx defaults to 9, and grid.ny defaults to whatever value is passed to grid.nx. Setting both values to 0 will remove the grid entirely. The number of ticks is approximate as this value is passed to pretty() to determine nice-looking, round breakpoints.

npoints

A dot is placed every npoints along each full trajectory. For hourly back trajectories points are plotted every npoint hours. This helps to understand where the air masses were at particular times and get a feel for the speed of the air (points closer together correspond to slower moving air masses). If npoints = NA then no points are added.

origin

If true a filled circle dot is shown to mark the receptor point.

plot

Should a plot be produced? FALSE can be useful when analysing data to extract plot components and plotting them in other ways.

...

other arguments are passed to cutData and scatterPlot. This provides access to arguments used in both these functions and functions that they in turn pass arguments on to. For example, plotTraj passes the argument cex on to scatterPlot which in turn passes it on to the lattice function xyplot where it is applied to set the plot symbol size.

Details

Several types of trajectory plot are available. trajPlot by default will plot each lat/lon location showing the origin of each trajectory, if no pollutant is supplied.

If a pollutant is given, by merging the trajectory data with concentration data (see example below), the trajectories are colour-coded by the concentration of pollutant. With a long time series there can be lots of overplotting making it difficult to gauge the overall concentration pattern. In these cases setting alpha to a low value e.g. 0.1 can help.

The user can also show points instead of lines by plot.type = "p".

Note that trajPlot will plot only the full length trajectories. This should be remembered when selecting only part of a year to plot.

Author

David Carslaw

Examples


# show a simple case with no pollutant i.e. just the trajectories
# let's check to see where the trajectories were coming from when
# Heathrow Airport was closed due to the Icelandic volcanic eruption
# 15--21 April 2010.
# import trajectories for London and plot
if (FALSE) { # \dontrun{
lond <- importTraj("london", 2010)
# well, HYSPLIT seems to think there certainly were conditions where trajectories
# orginated from Iceland...
trajPlot(selectByDate(lond, start = "15/4/2010", end = "21/4/2010"))
} # }

# plot by day, need a column that makes a date
if (FALSE) { # \dontrun{
lond$day <- as.Date(lond$date)
trajPlot(selectByDate(lond, start = "15/4/2010", end = "21/4/2010"),
  type = "day"
)
} # }

# or show each day grouped by colour, with some other options set
if (FALSE) { # \dontrun{
trajPlot(selectByDate(lond, start = "15/4/2010", end = "21/4/2010"),
  group = "day", col = "turbo", lwd = 2, key.pos = "right", key.col = 1
)
} # }
# more examples to follow linking with concentration measurements...