Dear list,
A common addition to any spatial plot are a north arrow and a scale bar.
I've searched online for a straightforward way to add those to a ggplot
plot. I then decided to give a go myself. A crude first attempt for an
automatic scalebar addition function is listed below. The example works
for the meuse dataset, but a second with a different dataset did yield
good results.
My question to you is: is there anyone who has some good tips / example
code to add a north arrow and a scalebar to a ggplot image. Any
expansions on the code below are also welcome.
cheers,
Paul
ps Some info on my system is listed at the very bottom
library(sp)
library(ggplot2)
data(meuse)
data(meuse.grid)
string.length = function(s) {
# browser()
if(!is.character(s)) s = as.character(s)
length(strsplit(s, "")[[1]])
}
makeNiceNumber = function(num, num.pretty = 1) {
noNumbers = string.length(as.character(round(num)))
return(round(num / 10^(noNumbers - num.pretty)) * 10^(noNumbers -
num.pretty))
}
makeScaleBar = function(obj, plotname, xname = "x", yname = "y", unit =
"m", placement = "bottomright") {
# browser()
range_x = max(obj[[xname]]) - min(obj[[xname]])
range_y = max(obj[[yname]]) - min(obj[[yname]])
if(placement == "bottomright") {
xcoor.max = makeNiceNumber(max(obj[[xname]]) - (0.05 *range_x ),
string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
range_x)))
xcoor.min = makeNiceNumber(max(obj[[xname]]) - (0.5 *range_x ),
string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
range_x)))
ycoor = min(obj[[yname]]) + (0.05 * range_y)
} else {
xcoor.min = makeNiceNumber(max(obj[[xname]]) - (0.95 *range_x ),
string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
range_x)))
xcoor.max = makeNiceNumber(max(obj[[xname]]) - (0.5 *range_x ),
string.length(round(max(obj[[xname]]))) - string.length(round(0.3 *
range_x)))
ycoor = min(obj[[yname]]) + (0.95 * range_y)
}
scalebar.data = data.frame(x = c(xcoor.max, xcoor.min), y = ycoor,
lbl = c(paste(xcoor.max - xcoor.min, unit), 0))
scalebar.data[[plotname]] = min(obj[[plotname]])
return(list(geom_path(aes(x = x, y = y), data = scalebar.data, lwd =
2, color = "black"),
geom_text(aes(x = x, y = y, label = lbl), data =
scalebar.data, vjust = 1.3)))
}
sb = makeScaleBar(meuse.grid, "dist", placement = "topright")
ggplot(aes(x = x, y = y, fill = dist), data = meuse.grid) + geom_tile()
+ sb[[1]] + sb[[2]]
R version 2.12.0 (2010-10-15)
Platform: i486-pc-linux-gnu (32-bit)
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
[3] LC_TIME=en_US.UTF-8 LC_COLLATE=en_US.UTF-8
[5] LC_MONETARY=C LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-8 LC_NAME=C
[9] LC_ADDRESS=C LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
attached base packages:
[1] grid stats graphics grDevices utils datasets methods
[8] base
other attached packages:
[1] ggplot2_0.8.7 digest_0.4.2 reshape_0.8.3 plyr_0.1.9 proto_0.3-8
[6] sp_0.9-62
loaded via a namespace (and not attached):
[1] lattice_0.19-13
hiems...@fg-113:~$ uname -a
Linux fg-113 2.6.32-21-generic #32-Ubuntu SMP Fri Apr 16 08:10:02 UTC
2010 i686 GNU/Linux
--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: +3130 253 5773
http://intamap.geo.uu.nl/~paul
http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
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