Plot an image with a color palette, in a way that does not conflict with
layout(). To plot just a palette,
e.g. to get an x-y plot with points colored according to a palette, use
drawPalette() and then draw the main diagram.
imagep( x, y, z, xlim, ylim, zlim, zclip = FALSE, flipy = FALSE, xlab = "", ylab = "", zlab = "", zlabPosition = c("top", "side"), las.palette = 0, decimate = TRUE, quiet = FALSE, breaks, col, colormap, labels = NULL, at = NULL, drawContours = FALSE, drawPalette = TRUE, drawTriangles = FALSE, tformat, drawTimeRange = getOption("oceDrawTimeRange"), filledContour = FALSE, missingColor = NULL, useRaster, mgp = getOption("oceMgp"), mar, mai.palette, xaxs = "i", yaxs = "i", asp = NA, cex = par("cex"), cex.axis = cex, cex.lab = cex, cex.main = cex, axes = TRUE, main = "", axisPalette, add = FALSE, debug = getOption("oceDebug"), ... )
These have different meanings in different modes of operation.
Mode 1. One
mode has them meaning the locations of coordinates along which values
z are defined. In this case, both
must be supplied and, within each, the values must be finite and
distinct; if values are out of order, they (and
z) will be
transformed to put them in order.
ordered in a matching way).
z is provided but not
y, then the latter
are constructed to
indicate the indices of the matrix, in contrast
to the range of 0 to 1, as is the case for
Mode 3. If
x is a list, its components
x$y are used
y, respectively. If the list has component
z this is used for
z. (NOTE: these arguments are meant to
mimic those of
image(), which explains the same description
here.) Mode 4. There are also some special cases, e.g. if
x is a
topographic object such as can be created with
as.topo(), then longitude and latitude are used for
axes, and topographic height is drawn.
A matrix containing the values to be plotted (NAs are allowed). Note
that x can be used instead of z for convenience. (NOTE: these arguments
are meant to mimic those of
image(), which explains the same
Limits on x and y axes.
If missing, the z scale is determined by the range of the data.
zlim may take several forms. First, it may be a pair
of numbers that specify the limits for the color scale. Second,
it could be the string
"histogram", to yield a flattened
histogram (i.e. to increase contrast). Third, it could be the
"symmetric", to yield limits that are symmetric
about zero, which can be helpful in drawing velocity fields,
for which a zero value has a particular meaning (in which case,
a good color scheme might be
Logical, indicating whether to clip the colors to those
zlim. This only works if
provided. Clipped regions will be colored with
Thus, clipping an image is somewhat analogous to clipping in an xy
plot, with clipped data being ignored, which in an image means to be be
TRUE indicating that the graph
should have the y axis reversed, i.e. with smaller values at
the bottom of the page. (Historical note: until 2019 March 26,
the meaning of
flipy was different; it meant to reverse the
range of the y axis, so that if
ylim were given as a reversed
range, then setting
flipy=TRUE would reverse the flip, yielding
a conventional axis with smaller values at the bottom.)
Names for x axis, y axis, and the image values.
String indicating where to put the label for the z axis, either at the top-right of the main image, or on the side, in the axis for the palette.
Controls whether the image will be decimated before plotting, in three possible cases.
decimate=FALSE then every grid cell in the matrix will
be represented by a pixel in the image.
decimate=TRUE (the default), then decimation will be done
in the horizontal or vertical direction (or both) if the length of the
corresponding edge of the
z matrix exceeds 800. (This also creates
a warning message.) The decimation
factor is computed as the integer just below the ratio of
to 400. Thus, no decimation is done if the dimension is less than 800,
but if the dimension s between 800 and 1199, only every second grid
point is mapped to a pixel in the image.
decimate is an integer, then that
z is subsampled
seq.int(1L, dim(z), by=decimate) (as is
the same is done for the
decimate is a vector of two integers, the first is used for
the first index of
z, and the second is used for the second
logical value indicating whether to silence warnings that might occur if the image is being decimated.
The z values for breaks in the color scheme. If this is of
length 1, the value indicates the desired number of breaks, which is
pretty(), in determining clean break points.
colormap is provided, it takes precedence over
Either a vector of colors corresponding to the breaks, of length
1 plus the number of breaks, or a function specifying colors.
col is not provided, and if
colormap is also not provided, then
colormap is provided, it takes precedence over
A color map as created by
precedence over the present arguments
(All of the other contents of
colormap are ignored, though.)
colormap is provided, it takes precedence over
Optional vector of labels for ticks on palette axis (must
Optional vector of positions for the
Logical value indicating whether to draw contours on the image, and palette, at the color breaks. Images with a great deal of high-wavenumber variation look poor with contours.
Indication of the type of palette to draw, if any. If
drawPalette=TRUE, a palette is drawn at the right-hand side of the
main image. If
drawPalette=FALSE, no palette is drawn, and the
right-hand side of the plot has a thin margin. If
drawPalette="space", then no palette is drawn, but space is put in
the right-hand margin to occupy the region in which the palette would
have been drawn. This last form is useful for producing stacked plots
with uniform left and right margins, but with palettes on only some of
Logical value indicating whether to draw
triangles on the top and bottom of the palette. This is passed to
Logical, only used if the
x axis is a
TRUE, then an indication of the time range of the
data (not the axis) is indicated at the top-left margin of the
graph. This is useful because the labels on time axes only indicate
hours if the range is less than a day, etc.
Boolean value indicating whether to use filled contours to plot the image.
A color to be used to indicate missing data, or
NULL for transparent (to see this, try setting
A 3-element numerical vector to use for
par(mar), computed from this. The default is
tighter than the R default, in order to use more space for the
data and less for the axes.
A 4-element Value to be used with
("mar"). If not
given, a reasonable value is calculated based on whether
ylab are empty strings.
Palette margin corrections (in inches), added to the
mai value used for the palette. Use with care.
Character indicating whether image should extend to edge
of x axis (with value
"i") or not; see
xaxs but for y axis.
Aspect ratio of the plot, as for
x inherits from topo and
asp is redefined to be the reciprocal of the
mean latitude in
x, as a way to reduce geographical distortion.
asp is not
NA, then it is used directly.
numeric character expansion factor, used for
if those values are not supplied.
numeric character expansion factors for axis numbers,
axis names and plot titles; see
TRUE to get axes on the main image.
Title for plot.
Logical value indicating whether to add to an existing plot.
The default value,
FALSE indicates that a new plot is to be created.
TRUE, the idea is to add an image (but not
its palette or its axes) to an existing plot. Clearly, then, arguments
xlim are to be ignored. Indeed, if
add=TRUE, the only
arguments examined are
x (which must be a vector; the mode of providing
a matrix or
oce object does not work),
decimate, plus either
A flag that turns on debugging. Set to 1 to get a moderate amount of debugging information, or to 2 to get more.
Optional arguments passed to plotting functions.
A list is silently returned, containing
values that can be used by
oce.grid() to add a grid to the
By default, creates an image with a color palette to the right. The effect is similar to
filled.contour() except that with
imagep it is possible to
layout() outside the function, which enables the creation
of plots with many image-palette panels. Note that the contour lines may not
coincide with the color transitions, in the case of coarse images.
Note that this does not use
layout() or any of the other screen
splitting methods. It simply manipulates margins, and draws two plots
together. This lets users employ their favourite layout schemes.
imagep is an analogue of
image(), and from that
it borrows a the convention that the number of rows in the matrix corresponds to
x axis, not the
y axis. (Actually,
the length of
x to match either
here only the first is permitted.)
library(oce) # 1. simplest use imagep(volcano) # 2. something oceanographic (internal-wave speed) h <- seq(0, 50, length.out=100) drho <- seq(1, 3, length.out=200) speed <- outer(h, drho, function(drho, h) sqrt(9.8 * drho * h / 1024)) imagep(h, drho, speed, xlab="Equivalent depth [m]", ylab=expression(paste(Delta*rho, " [kg/m^3]")), zlab="Internal-wave speed [m/s]") # 3. fancy labelling on atan() function x <- seq(0, 1, 0.01) y <- seq(0, 1, 0.01) angle <- outer(x,y,function(x,y) atan2(y,x)) imagep(x, y, angle, filledContour=TRUE, breaks=c(0, pi/4, pi/2), col=c("lightgray", "darkgray"), at=c(0, pi/4, pi/2), labels=c(0, expression(pi/4), expression(pi/2))) # 5. y-axis flipping par(mfrow=c(2,2)) data(adp) d <- adp[["distance"]] t <- adp[["time"]] u <- adp[["v"]][ , ,1] imagep(t, d, u, drawTimeRange=FALSE) mtext("normal") imagep(t, d, u, flipy=TRUE, drawTimeRange=FALSE) mtext("flipy") imagep(t, d, u, ylim=rev(range(d)), drawTimeRange=FALSE) mtext("ylim") imagep(t, d, u, ylim=rev(range(d)), flipy=TRUE, drawTimeRange=FALSE) mtext("flipy and ylim") par(mfrow=c(1,1)) # 6. a colormap case data(topoWorld) cm <- colormap(name="gmt_globe") imagep(topoWorld, colormap=cm)