Contour matrix data and draw — xcontour • ximage

Like contour() but to work with ximage()

Usage

xcontour(x, extent = NULL, ..., add = FALSE)

Arguments

x

something we can contour

extent

optional, numeric xmin,xmax,ymin,ymax

...

Arguments passed on to ximage

zlim: optional, absolute range of data to map colours to (maintains comparable colours across plots); values outside display as 'na.col'; single-band numeric data only
xlab: x axis label, empty by default
ylab: y axis label, empty by default
col: colours to map single-band data to
breaks: a set of finite numeric breakpoints for the colours, one more break than colour (if not, colours are interpolated to fit)
alpha: optional constant opacity in [0, 1] (or vector/matrix, recycled) applied on top of any existing alpha channel; not supported for nativeRaster input
na.col: colour for missing values, default "transparent"

add

add to plot, or start afresh

Value

nothing, called for its side effect of creating or adding to a plot

Details

Input may be a matrix or a list from gdal_raster_data() in the vapour package or from read_ds() in the gdalraster package.

Examples

#EPSG:27200 see https://github.com/mdsumner/volcano
ex <- c(2667400, 2668010, 6478700, 6479570)
v <- volcano[nrow(volcano):1, ncol(volcano):1]
ximage(v, extent = ex, asp = 1)

xcontour(v, add = TRUE, extent = ex, col = "white")
xrect(ex, add = TRUE, border = "hotpink", lwd = 5)