On 01/21/2013 08:59 AM, Murat Tasan 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?
Hi Murat,
"User units" are the units of the plot itself. If you have very large
differences between the x and y units of a plot, functions like
"draw.circle" will try to adjust for this when drawing the circle.
Currently draw.circle uses the x units of the plot for the radius and
adjusts the y units. So if you asked for a circle on a plot with the
user units above - xlim=c(0,1),ylim=c(0,1000000) - with a radius of 0.5
and centered at 0.5,500000, the circle would fill almost the whole plot.
In contrast, if you reverse the ratio, you would have to ask for a
radius of 50 just to see a dot in the middle of the plot.
I had a quick look for a definition of "user units" and found that "user
coordinates" is used several times in the documentation for the "par"
function. However, I could not find a definition other than the implicit
one of the coordinates or units that the user specifies for a plot.
Jim
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