Label the cells of a matrix in place

Draw the values of a matrix as text labels, each at the centre of its cell in the same layout used by ximage(). The first cell of the matrix is the top-left label, and each row of the matrix is a line of labels reading left to right down the page ("raster order").

Usage

xtext(x, extent = NULL, add = FALSE, cex = NULL, fit = 0.9, ...)

Arguments

x: a matrix of values to draw as labels, or a reader-output list
extent: optional, numeric xmin,xmax,ymin,ymax (defaults to the 0,ncol 0,nrow index space of the matrix)
add: add to plot, or start afresh
cex: text size, computed to fit the cells if not supplied
fit: fraction of the cell the largest label should occupy when 'cex' is computed, default 0.9
...: arguments passed to text(), for example 'col'

Value

invisibly, a list with 'x', 'y' (label positions), 'labels', and 'cex' as used

Details

Text size is chosen automatically to fit the largest label within a cell, scaled by 'fit' (use 'cex' to override). Labels that are NA are not drawn.

Input may be a matrix (values are used as labels via format()), or a list in the style of vapour or gdalraster reader output (a row-major vector with 'dimension'/'extent' attributes, or a 'gis' attribute).

Examples

m <- matrix(1:12, 3, byrow = TRUE)
ximage(m)
xtext(m, add = TRUE)


## the label positions are cell centres in the extent
ximage(volcano, extent = c(0, 1, 0, 1))
xtext(volcano[seq(1, 87, by = 8), seq(1, 61, by = 6)],
      extent = c(0, 1, 0, 1), add = TRUE, col = "white")