[R-sig-Geo] How to draw a map as PDF which shows the exact given view port only and without any border (PDF crop)

[Hans-Jörg Bibiko]

Hi,

I tried to find an answer in the net but up to now without success.

A simple example made with:

R version 2.10.0 (2009-10-26) 
x86_64-apple-darwin9.8.0 

locale:
[1] C/en_US.UTF-8/C/C/C/C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     


My task is to draw a map as PDF of Portugal. My view port is given by the coordinates xlim <- c(-10, -6) and ylim <- c(36.9, 42.5). The width of the viewport has to be 5in (for a publication). Due to the ratio of xlim and ylim the height is 7in. OK.


I tried:

# ________________________________________

library(maptools)
data(wrld_simpl)

# my view port
xlim <- c(-10, -6)
ylim <- c(36.9, 42.5)

pdf(file = "map_1.pdf", width = 5, height = 7, bg = "azure2")
plot(wrld_simpl, xlim = xlim, ylim = ylim, col = "khaki")

# my actual view port as reference
rect(xlim[1], ylim[1], xlim[2], ylim[2], border = "red")

dev.off()

# ________________________________________


and ended up in Figure 1 (see attachment). My view port is shown as a red rectangle. As you can see the PDF contains more as I expected. 



After some empirical attempts I came up with a wrapper function "pdfNoBorder". Thus I tried it again with that function:

# ________________________________________

library(maptools)
data(wrld_simpl)

pdfNoBorder <- function(file, width, height, xlim, ylim, 
	asp = 1, ...) {
	if (missing(width) && missing(height)) {
		stop("At least width or height must be given")
	}
	if (missing(xlim) && missing(ylim)) {
		stop("xlim and ylim must be given")
	}
	if (missing(width)) {
		width = diff(xlim)/diff(ylim) * height
	}
	if (missing(height)) {
		height = width/(diff(xlim)/diff(ylim))
	}
	pdf(file = file, width = width, height = height, ...)
	par(mai = rep(0, 4))
	plot.new()
	par(fin = c(width * 1.08, height * 1.08), new = T) ### !!!!!
	plot.window(xlim = xlim, ylim = ylim, asp = asp)
}

# my view port
xlim <- c(-10, -6)
ylim <- c(36.9, 42.5)

pdfNoBorder(file = "map_2.pdf", width = 5, xlim = xlim, ylim = ylim, 
	bg = "azure2")
plot(wrld_simpl, add = TRUE, col = "khaki")
rect(xlim[1], ylim[1], xlim[2], ylim[2], border = "red")
dev.off()

# ________________________________________

and Figure 2 shows the result. So far so good, but if you look at the "pdfNoBorder" function I have to use "an empirical hack" namely the line:

par(fin = c(width * 1.08, height * 1.08), new = T)

The value 1.08 works "quite well" but I think that this value is a function of width, height, and the ratio width/height or similar and - of course - it's not precisely.


My question is now whether somebody could give my an hint how to draw a PDF map which shows ONLY my desired view port and without any border by using a "clean" way without any estimated values.


Many thanks in advance,

--Hans



Figure 1
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Figure 2
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