Plot an image on an existing map that was created with mapPlot().
mapImage(
longitude,
latitude,
z,
zlim,
zclip = FALSE,
breaks,
col,
colormap,
border = NA,
lwd = par("lwd"),
lty = par("lty"),
missingColor = NA,
filledContour = FALSE,
gridder = "binMean2D",
debug = getOption("oceDebug")
)numeric vector of longitudes corresponding to z
matrix.
numeric vector of latitudes corresponding to z
matrix.
numeric matrix to be represented as an image.
limit for z (color).
A logical value, TRUE indicating that out-of-range
z values should be painted with missingColor and FALSE
indicating that these values should be painted with the nearest
in-range color. If zlim is given then its min and max set the
range. If zlim is not given but breaks is given, then the min
and max of breaks sets the range used for z. If neither zlim
nor breaks is given, clipping is not done, i.e. the action is as
if zclip were FALSE.
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 supplied to pretty(), in determining clean break points.
Either a vector of colors corresponding to the breaks,
of length 1 plus the number of breaks, or a function specifying
colors, e.g. oce.colorsViridis() for the Viridis scheme.
optional colormap, as created by colormap(). If a
colormap is provided, then its properties takes precedence over
breaks, col, missingColor, and zclip specified to
mapImage.
Color used for borders of patches (passed to
polygon()); the default NA means no border.
line width, used if borders are drawn.
line type, used if borders are drawn.
a color to be used to indicate missing data, or
NA to skip the drawing of such regions (which will retain
whatever material has already been drawn at the regions).
an indication of whether to use filled
contours. This may be FALSE (the default), TRUE, or a positive
numerical value. If FALSE, then polygons are used. Otherwise, the
longitude-latitude values are transformed to x-y values, which will
not be on a grid and thus will require gridding so that
.filled.contour() can plot the filled contours. The method used
for gridding is set by the gridder parameter (see next item). If
filledContour is TRUE, then the grid is constructed with the aim
of having approximately 3 of the projected x-y points in each cell.
That can leave some cells unoccupied, yielding blanks in the drawn
image. There are two ways around that. First, the gridder can
be set up to fill gaps. Second, a numerical value can be used for
filledContour. For example, using filledContour equal to 1.5
will increase grid width and height by a factor of 1.5, which may
be enough to fill all the gaps, depending on the projection and the
area shown.
specification of how gridding is to be done, used
only if filledContour is TRUE. The value of gridder may
"binMean2D", which is the default, "interp", or a function. In
the first two cases, the gridding is done with either binMean2D()
or interp::interp(), respectively. For more on the last case, see
“Details”.
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 one function calls another, it usually reduces the value of
debug first, so that a user can often obtain deeper debugging
by specifying higher debug values.
Until oce 1.7.4, the gridder argument could be set to "akima",
which used the akima package. However, that package is not
released with a FOSS license, so CRAN requested a change to
interp. Note that drawImage() intercepts the errors
that sometimes get reported by interp::interp().
library(oce)
data(coastlineWorld)
data(topoWorld)# Northern polar region, with color-coded bathymetry par(mfrow = c(1, 1), mar = c(2, 2, 1, 1)) cm <- colormap(zlim = c(-5000, 0), col = oceColorsGebco) drawPalette(colormap = cm) mapPlot(coastlineWorld, projection = "+proj=stere +lat_0=90", longitudelim = c(-180, 180), latitudelim = c(70, 110) ) # Uncomment one of the next four blocks. See # https://dankelley.github.io/dek_blog/2024/03/07/mapimage.html # for illustrations.
# Method 1: the default, using polygons for lon-lat patches mapImage(topoWorld, colormap = cm)
# Method 2: filled contours, with ugly missing-data traces # mapImage(topoWorld, colormap = cm, filledContour = TRUE)
# Method 3: filled contours, with a double-sized grid cells # mapImage(topoWorld, colormap = cm, filledContour = 2)
# Method 4: filled contours, with a gap-filling gridder) # g <- function(...) binMean2D(..., fill = TRUE, fillgap = 2) # mapImage(topoWorld, colormap = cm, filledContour = TRUE, gridder = g)
mapGrid(15, 15, polarCircle = 1, col = gray(0.2)) mapPolygon(coastlineWorld[["longitude"]], coastlineWorld[["latitude"]], col = "tan" )
Dan Kelley
Image data are on a regular grid in lon-lat space, but not in the
projected x-y space. This means that image() cannot be used.
Instead, there are two approaches, depending on the value of
filledContour.
If filledContour is FALSE, the image "pixels" are drawn with
polygon(). This can be prohibitively slow for fine grids.
However, if filledContour is TRUE, then the "pixels" are
remapped into a regular grid and then displayed with
.filled.contour(). The remapping starts by converting the
regular lon-lat grid to an irregular x-y grid using lonlat2map().
This irregular grid is then interpolated onto a regular x-y grid in
accordance with the gridder parameter. If gridder values of
"binMean2D" and "interp" do not produce satisfactory results,
advanced users might wish to supply a function to do the gridding
according to their own criteria. The function must have as its
first 5 arguments (1) an x vector, (2) a y vector, (3) a z matrix
that corresponds to x and y in the usual way, (4) a vector holding
the desired x grid, and (5) a vector holding the desired y grid.
The return value must be a list containing items named xmids,
ymids and result. To understand the meaning of the parameters
and return values, consult the documentation for binMean2D().
Here is an example of a scheme that will fill data gaps of 1 or 2
cells:
g <- function(...) binMean2D(..., fill = TRUE, fillgap = 2)
mapImage(..., gridder = g, ...)
A map must first have been created with mapPlot().
Other functions related to maps:
formatPosition(),
lonlat2map(),
lonlat2utm(),
map2lonlat(),
mapArrows(),
mapAxis(),
mapContour(),
mapCoordinateSystem(),
mapDirectionField(),
mapGrid(),
mapLines(),
mapLocator(),
mapLongitudeLatitudeXY(),
mapPlot(),
mapPoints(),
mapPolygon(),
mapScalebar(),
mapText(),
mapTissot(),
oceCRS(),
oceProject(),
shiftLongitude(),
usrLonLat(),
utm2lonlat()