"user units" in plotrix
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