Loading PNG files directly from URL

Question

I am using the png package to load PNGs as raster images, and then plotting them. The PNGs are coming from an online source, namely, Wikipedia. I can get the following to work:

library(png)

pngURL <- "http://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Flag_of_Afghanistan.svg/150px-Flag_of_Afghanistan.svg.png"

# Works:
download.file(pngURL, "temp.png", mode = "wb")
localPNG <- readPNG("temp.png")
plot(1)
rasterImage(localPNG, 0.8, 0.8, 1.2, 1.2)

However, rather than use download.file() to store the PNG locally, then re-loading it, it would be preferable to load the PNG directly from the URL. However, this does not work:

# Does not work:
internetPNG <- readPNG(pngURL)

As it results in

Error in readPNG(pngURL) : 
  unable to open http://upload.wikimedia.org/wiki...

Does anyone have suggestions for how to get this to work, or are there particular reasons that R won't load this PNG from a URL?

Thanks in advance.

Answer 1

Use getURLcontent in the RCurl package.

library(RCurl)
myurl <- "http://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Flag_of_Afghanistan.svg/150px-Flag_of_Afghanistan.svg.png"
my_image <-  readPNG(getURLContent(myurl))