adding contour lines to a filled.contour

Andy Bunn wrote:

Hi all,

Does anybody know how to add contour lines to a filled contour plot?

I want to draw a single contour around values that are above a certain
level (e.g., significant). The problem I'm having is that since the
filled.contour command actually draws two plots (data and the key),
adding contour lines paints them over both plots.

Any suggestions?

Yes. Look into the code of filled.contour(), how things are set up for
those two parts of the plot. The following solution will become clear:

 # your code:
 junk.mat <- matrix(rnorm(1600), 16, 100)
 filled.contour(junk.mat, color = terrain.colors)
 contour.mat <- ifelse(junk.mat < 2, 0, junk.mat)

 # insert 3 lines of code, stolen from filled.contour():
 mar.orig <- par("mar")
 w <- (3 + mar.orig[2]) * par("csi") * 2.54
 layout(matrix(c(2, 1), nc = 2), widths = c(1, lcm(w)))

 # your code:
 contour(contour.mat, levels = 1, drawlabels = FALSE, 
     axes = FALSE, frame.plot = FFALSE, add = TRUE)
 

Uwe Ligges

Thanks, Andy

#~~~~~~~~~~~~~~~~~~~
#example

junk.mat <- matrix(rnorm(1600), 16, 100)

filled.contour(junk.mat,
               color = terrain.colors)

#set values < 2 to zero
contour.mat <- ifelse(junk.mat < 2, 0, junk.mat)

#add contours
contour(contour.mat,
        levels = 1,
        drawlabels = F,
        axes = F,
        frame.plot = F,
        add = T)