Question

How can I use the lwd to represent some quantity?

For instance:

plot(NULL, type="n", xlim=c(4,7), ylim=c(1,6), xlab="", ylab="")
points(c(5.25,5.25), c(4,5), type="l", lwd=87)
points(c(5.5,6.5), c(3.5,3.5), type="l", lwd=92)
rect(5,3,5.5,4, col="white")

I want the lines drawn with the points functions exactly as wide/tall as the rectangle. The values 87 and 92 above I found manually. Is there a way to calculate those quantities?

EDIT:
The background for the question is: I want to draw bezier curves, and I want the thickness of the curve represent my data. My first idea was to use lwd for that. Can I do better?

Answer 1

lwd is the wrong tool for what you’re trying to do. The actual line width will change relative to user coordinates depending on how your plot window is resized (or the dimensions when you save it). You obviously know about the rect command, why not just use that? You might also look into the shape package.

–Edit–

For more complex shapes, my experience doesn’t extend beyond polygon. With that, you could get the coordinates bc for a Bezier curve, and then draw a polygon around x = c(bc$x + dx, rev(bc$x - dx), y = c(bc$y + dy, rev(bc$y - dy), but I’m not sure how well that would look for a complex curve.

As an aside, you can replace points(..., type = "l") with lines(...) if you’d like. (I think it makes my code more readable.)