Question

I have a distance sequence, which I would like to plot of a line in spatstat. Example:

library(spatstat)

x <- c(0.3, 5)
y <- c(3, 1.2)

range.x <- c(0, max(x)+0.2)
range.y <- c(0, max(y)+0.2)

owin <- owin(range.x, range.y)
the.line <- psp(x0 = x[1],x1 = x[2],y0 = y[1],y1 = y[2], window = owin)

plot(the.line)    

seqs <- data.frame(name = seq(1,7), distance = c(0.12, 0.3, 0.45, 0.5, 0.7, 0.89, 0.95))
lengths <- seqs$distance*lengths.psp(the.line)

I would like to plot lengths on top of the.line using seqs$name as labels in a following way (labels added with Illustrator):

Would anyone know how to do this? Help would be very much appreciated!

Answer 1

The text function will allow you to add text to an existing plot. Whether you can rotate the text or not depends on the graphics device that you are using, see ?par sections on ‘crt’ and ‘srt’. Also see the ‘adj’ argument to text for how to get the text above the line rather than obscuring the line.

This all assumes that the plotting is being done in base graphics.

The following worked for me on windows (using the default windows graphics device) after running the code above:

x.new <- seqs$distance*x[2] + (1-seqs$distance)*x[1]
y.new <- seqs$distance*y[2] + (1-seqs$distance)*y[1]

tmp.x <- grconvertX(x, to='inches')
tmp.y <- grconvertY(y, to='inches')
theta <- atan2(diff(tmp.y),diff(tmp.x))*180/pi

text( x.new, y.new, seqs$name, adj=c(0,0), srt=theta )