If you want to convert between different units using base graphics then
look at the grconvertX and grconvertY functions (in the graphics package).
 These functions will convert from/to user coordinates, inches, device,
figure, and plot coordinates.  So you could use grconvertX to  find out
what user value on the x scale to give to draw.circle that would then
generate a circle with a given size in inches, or relative to the device,
figure, or plotting region.


On Sun, Jan 20, 2013 at 2:59 PM, Murat Tasan <mmuurr@gmail.com> wrote:

> hi all - i'm having some difficulty figuring out how to convert
> between "user units" (which i can't find a definition for in the
> plotrix package) and either (a) device units (e.g. inches with PDFs)
> or (b) user coordinates along any particular axis.
>
> as an example, suppose i set up a PDF device with inches, the device
> has both outer and inner magins, and the plot region has drastically
> different x and y coordinate ranges (e.g. xlim = c(0, 1), ylim =  c(0,
> SOME_VERY_LARGE_NUMBER)).
>
> now i'd like to draw.circle(...) but i can't figure out what units the
> radius argument takes.
> "user units" doesn't appear to be inches in this case, and it it
> corresponds to user coordinates, i don't know which axis' scaling is
> to be used as the reference.
>
> ideally, one would be able to specify the radius in user coordinates
> while specifying _which_ axis to use as the standard (e.g. an axis =
> "y" or axis = "x" argument).
>
> getFigCtr(...) can help in figuring this out, but its argument takes
> the relative position of the "figure" region, rather than the "plot"
> region, which is more apt for properly placing shapes.
>
> i know the grid package has extensive unit conversion code, but i'm
> trying to update a series of figures using only base graphics...
>
> i can't seem to find a rigorous definition of "user units" anywhere in
> the plotrix package.
> anyone know of where i can find this info?
>
> cheers,
>
> -m
>
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-- 
Gregory (Greg) L. Snow Ph.D.
538280@gmail.com

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