"user units" in plotrix

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 at 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

--
Gregory (Greg) L. Snow Ph.D.
538280 at gmail.com