R: Trajectory line plots with conditioning

trajPlot {openair} | R Documentation

## Trajectory line plots with conditioning

### Description

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.alpha = 0.4,
      projection = "lambert",
      parameters = c(51, 51),
      orientation = c(90, 0, 0),
      grid.col = "deepskyblue",
      npoints = 12,
      origin = 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.alpha` | The transpency 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.
`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"`.
`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 togther 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.
`...` | 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 aslo 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(s)

David Carslaw

### See Also

`importTraj` to import trajectory data from the King's College server and `trajLevel` for trajectory binning functions.

### 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
    ## Not run:
    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"))
    ## End(Not run)

    # plot by day, need a column that makes a date
    ## Not run:
    lond$day <- as.Date(lond$date)
    trajPlot(selectByDate(lond, start = "15/4/2010", end = "21/4/2010"),
    type = "day")

    ## End(Not run)

    # or show each day grouped by colour, with some other options set
    ## Not run:
     trajPlot(selectByDate(lond, start = "15/4/2010", end = "21/4/2010"),
    group = "day", col = "jet", lwd = 2, key.pos = "right", key.col = 1)

    ## End(Not run)
    # more examples to follow linking with concentration measurements...

[Package openair version 2.8-5 Index]