CODEWITHSUNDEEP
rvisualizationcontour
Marc in the box
Marc in the box

Reputation: 12005

How to add math symbols to contour label

I can't seem to pass math symbols to a contour label. Is this possible?

Example:

image(volcano)
contour(volcano, level=150, add=TRUE, label = "150") # works
contour(volcano, level=120, add=TRUE, label = expression(alpha)) # doesn't work
contour(volcano, level=110, add=TRUE, label = bquote(alpha)) # doesn't work
text(0.5,0.5, labels = bquote(alpha == .(120))) # works
text(0.2,0.5, labels = expression(paste(alpha, "= 150"))) # works

enter image description here

Upvotes: 2

Views: 139

Answers (1)

Maurits Evers
Maurits Evers

Reputation: 50718

Here is a solution:

image(volcano);
levels <- c(150, 120, 110);
for (i in 1:length(levels)) {
    contour(
        volcano, add = TRUE,
        level = levels[i], 
        label = sprintf("a = %i", levels[i]), 
        vfont = c("sans serif symbol", "plain"), labcex = 1);
}

enter image description here

The key here is to use vfont to force Hershey vector fonts instead of the current font family. You can then use the "HersheySansSymbol" font family to typeset "a" as "α", by using the contour function argument vfont = c("sans serif symbol", "plain"). It's a bit hidden, but more details on the Hershey fonts can be found in ?Hershey.

PS. You can also use a seriffed bold font with vfont = c("serif symbol", "bold").

Upvotes: 3

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