plot,section-method: Plot a Section

Description

Creates a summary plot for a CTD section, with one panel for each value of which.

Usage

# S4 method for section
plot(x, which = c(1, 2, 3, 99), eos, at = NULL,
  labels = TRUE, grid = FALSE, contourLevels = NULL,
  contourLabels = NULL, stationIndices, coastline = "best",
  xlim = NULL, ylim = NULL, zlim = NULL, map.xlim = NULL,
  map.ylim = NULL, clongitude, clatitude, span, projection = NULL,
  xtype = "distance", ytype = "depth", ztype = "contour",
  zbreaks = NULL, zcol = NULL, legend.loc = "bottomright",
  showStations = FALSE, showStart = TRUE, showBottom = TRUE,
  axes = TRUE, mgp, mar, col, cex, pch, labcex = 1, debug, ...)

Arguments

a section object, e.g. as created by as.section or read.section.

which

a list of desired plot types, as explained in “Details”. There may be up to four panels in total, and the desired plots are placed in these panels, in reading order. If only one panel is plotted, par is not adjusted, which makes it easy to add to the plot with subsequent plotting commands.

eos

Character indication of the seawater equation of state to use. The permitted choices are "gsw" and "unesco". If eos is not supplied, it defaults to getOption("oceEOS", default="gsw").

If NULL (the default), the x axis will indicate the distance of the stations from the first in the section. (This may give errors in the contouring routine, if the stations are not present in a geographical order.) If a list, then it indicates the values at which stations will be plotted.

labels

Either a logical, indicating whether to put labels on the x axis, or a vector that is a list of labels to be placed at the x positions indicated by at.

grid

If TRUE, points are drawn at data locations.

contourLevels

Optional contour levels.

contourLabels

Optional contour labels.

stationIndices

Optional list of the indices of stations to use. Note that an index is not a station number, e.g. to show the first 4 stations, use station.indices=1:4.

coastline

String giving the coastline to be used in a station map The permitted choices are "best" (the default) to pick a variant that suits the scale, "coastlineWorld" for the coarse version that is provided by oce, "coastlineWorldMedium" or "coastlineWorldFine" for two coastlines provided by the ocedata package, or "none", to avoid drawing a coastline.

xlim

Optional limit for x axis (only in sections, not map).

ylim

Optional limit for y axis (only in sections, not map)

zlim

Optional two-element numerical vector specifying the limit on the plotted field. This is used only if ztype="image"; see also zbreaks and zcol.

map.xlim, map.ylim

Optional limits for station map; map.ylim is ignored if map.xlim is provided.

clongitude, clatitude, span

Optional map centre position and span (km).

projection

Parameter specifying map projection; see mapPlot. If projection="automatic", however, a projection is devised from the data, with stereographic if the mean latitude exceeds 70N and mollweide otherwise.

xtype

Type of x axis, for contour plots, either "distance" for distance (in km) to the first point in the section, "track" for distance along the cruise track, "longitude", "latitude", or "time". Note that if the x values are not in order, they will be put in order (which may make no sense) and a warning will be printed.

ytype

Type of y axis for contour plots, either "pressure" for pressure (in dbar, with zero at the surface) or "depth" for depth (in m below the surface, calculated from pressure with swDepth).

ztype

String indicating whether to how to indicate the "z" data (in the R sense, i.e. this could be salinity, temperature, etc; it does not mean the vertical coordinate) The choices are: "contour" for contours, "image" for an image (drawn with imagep with filledContours=TRUE), or "points" to draw points. In the first two cases, the data must be gridded, with identical pressures at each station.

zbreaks, zcol

Indication of breaks and colors to be used if ztype="points" or "image". If not provided, reasonable default are used. If zlim is given but breaks is not given, then breaks is computed to run from zlim[1] to zlim[2]. If zcol is a function, it will be invoked with an argument equal to 1+length(zbreaks).

legend.loc

Location of legend, as supplied to legend, or set to the empty string to avoid plotting a legend.

showStations

Logical indicating whether to draw station numbers on maps.

showStart

Logical indicating whether to indicate the first station with a different symbol than the others.

showBottom

An indication of whether (and how) to indicate the ocean bottom. If FALSE, then the bottom is not rendered. If TRUE, then it is rendered with a gray polygon. If showBottom is a character string, then there are three possibilities: is the string is "polygon" then a polygon is drawn, if it is "lines" then a line is drawn, and if it is "points" then points are drawn. If showBottom is an object inheriting from topo-class then the station locations are interpolated to that topography and the results are shown with a polygon. In this last case, the interpolation is set at a grid that is roughly in accordance with the resolution of the latitudes in the topo object. See “Examples”.

axes

Logical value indicating whether to draw axes.

mgp

A 3-element numerical vector to use for par(mgp), and also for par(mar), computed from this. If not provided, this defaults to getOption("oceMgp").

mar

Value to be used with par("mar"). If not provided, a default is set up.

col

Color, which defaults to par("col").

cex

Numerical character-expansion factor, which defaults to par("cex").

pch

Indication of symbol type; defaults to par("pch").

labcex

Size of characters in contour labels (passed to contour).

debug

an integer specifying whether debugging information is to be printed during the processing. This is a general parameter that is used by many oce functions. Generally, setting debug=0 turns off the printing, while higher values suggest that more information be printed. If debug is not supplied, it defaults to getOption("oceDebug").

...

Optional arguments passed to the contouring function.

Value

If the original section was gridded, the return value is that section. Otherwise, the gridded section that was constructed for the plot is returned. In both cases, the value is returned silently. The purpose of returning the section is to enable subsequent processing of the grid, including adding elements to the plot (see example 5).

Details

The type of plot is governed by which, as follows.

which=0 or "potential temperature" for temperature contours
which=1 or "temperature" for temperature contours (the default)
which=2 or "salinity" for salinity contours
which=3 or "sigmaTheta" for sigma-theta contours
which=4 or "nitrate" for nitrate concentration contours
which=5 or "nitrite" for nitrite concentration contours
which=6 or "oxygen" for oxygen concentration contours
which=7 or "phosphate" for phosphate concentration contours
which=8 or "silicate" for silicate concentration contours
which=9 or "u" for eastward velocity
which=10 or "uz" for vertical derivative of eastward velocity
which=11 or "v" for northward velocity
which=12 or "vz" for vertical derivative of northward velocity
which=20 or "data" for a dot for each data location
which=99 or "map" for a location map

The y-axis for the contours is pressure, plotted in the conventional reversed form, so that the water surface appears at the top of the plot. The x-axis is more complicated. If at is not supplied, then the routine calculates x as the distance between the first station in the section and each of the other stations. (This will produce an error if the stations are not ordered geographically, because the contour routine cannot handle non-increasing axis coordinates.) If at is specified, then it is taken to be the location, in arbitrary units, along the x-axis of labels specified by labels; the way this works is designed to be the same as for axis.

Examples

Run this code

# NOT RUN {
library(oce)
data(section)
sg <- sectionGrid(section)

## 1. start of section, default fields.
plot(head(section))

## 2. Gulf Stream
GS <- subset(section, 109<=stationId&stationId<=129)
GSg <- sectionGrid(GS, p=seq(0, 2000, 100))
plot(GSg, which=c(1, 99), map.ylim=c(34, 42))
par(mfrow=c(2, 1))
plot(GS, which=1, ylim=c(2000, 0), ztype='points',
     zbreaks=seq(0,30,2), pch=20, cex=3)
plot(GSg, which=1, ztype='image', zbreaks=seq(0,30,2))

par(mfrow=c(1, 1))

## 3. Image, with colored dots to indicate grid-data mismatch.
# }
# NOT RUN {
plot(GSg, which=1, ztype='image')
T <- GS[['temperature']]
col <- oceColorsJet(100)[rescale(T, rlow=1, rhigh=100)]
points(GS[['distance']],GS[['depth']],pch=20,cex=3,col='white')
points(GS[['distance']],GS[['depth']],pch=20,cex=2.5,col=col)
# }
# NOT RUN {

# }
# NOT RUN {
## 4. Image of Absolute Salinity, with 4-minute bathymetry
## It's easy to calculate the desired area for the bathymetry,
## but for brevity we'll hard-code it. Note that download.topo()
## caches the file locally.
f <- download.topo(west=-80, east=0, south=35, north=40, resolution=4)
t <- read.topo(f)
plot(section, which="SA", xtype="longitude", ztype="image", showBottom=t)
# }
# NOT RUN {
# }
# NOT RUN {
## 5. Temperature with salinity added in red
s <- plot(section, which="temperature")
distance <- s[["distance", "byStation"]]
depth <- s[["station", 1]][["depth"]]
salinity <- matrix(s[["salinity"]], byrow=TRUE, nrow=length(s[["station"]]))
contour(distance, depth, salinity, col=2, add=TRUE)
# }
# NOT RUN {
# }

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