Dear all,

I am trying to find a way to reliably and programmatically establish the
resolution (i.e. DPI or equivalent) of an on-screen device. It seemed to me
that

  dev.new(width=1, height=1)
  dpi <- dev.size("px")

would do the trick, but the result does not seem to be correct, at least on
OS X 10.9.1 using the "quartz" device. Specifically, the window that
appears is 1 inch square, as expected, but the result from dev.size() is
c(72,72), which isn't correct. My display is 1440x900, but if I call

  dev.new(width=720/72, height=450/72)

the resulting device fills much more than half the screen. But R gets the
size right in inches, so it, or something it calls, must presumably know
the real DPI value.

So, could anyone tell me whether there is a reliable way to determine DPI,
please?

All the best,
Jon

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