On 14/01/2014 15:32, Jon Clayden wrote:
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.
It is correct: you need to read what it actually claims to do.
units: the units in which to return the value - inches, cm, or
pixels (device units).
The device units are nominal pixels: they may or may not be actual ones.
PDF (as used by Quartz) has a nominal 72 pixels per inch irrespective
of display.
> 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?
No. And even when the OS reports this, it is often wrong.
--
Brian D. Ripley, rip...@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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