直接从URL加载PNG文件 [英] Loading PNG files directly from URL

问题描述

我正在使用png包将PNG加载为光栅图像，然后绘制它们. PNG来自在线资源，即Wikipedia.我可以进行以下工作:

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)

但是，与其直接使用download.file()在本地存储PNG，然后重新加载，不如直接从URL加载PNG.但是，这不起作用:

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)

因为它导致

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

是否有人对如何使其正常工作提出建议，还是有某些特殊原因导致R无法从URL加载此PNG?

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?

谢谢.

推荐答案

在RCurl程序包中使用getURLcontent.

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))

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