R：如何删除图中的微小轴边距

Question

I want to get rid the small margin close to zero on X and Y value (red line on pic), and plot ONLY what is showed in red square.

I tried setting par(mar = rep(0, 4) and xlim=c(0, ...) , ylim=c(0, ...) but R still keeps adding this tiny margin. How to get rid of it?

EDIT: another point of view on my problem: after running:

require(plotrix)
axisRange <- c(0,500)
plot(NULL, xlim = axisRange, ylim=axisRange)
draw.circle(0, 0, 200, col = "white", border = "red")

I end up with a circle positioned not in "true" 0,0 point:

EDIT2: Actually what I want to do, is to plot circles of different radius, and save it as an image. That is why I care about the margins. I end up with something like this (spots on the corners are for the reference):

And should be more like this:

Answer 1

You can set the xaxs and yaxs arguments to "i" as opposed to the default of "r". From the par help page:

Style "r" (regular) first extends the data range by 4 percent at each end and then finds an axis with pretty labels that fits within the extended range.

Style "i" (internal) just finds an axis with pretty labels that fits within the original data range.

library(plotrix)
axisRange <- c(0,500)
par(mar = rep(0,4))
plot(NULL, xlim = axisRange, ylim=axisRange, xaxs = "i", yaxs = "i")
draw.circle(0, 0, 200, col = "white", border = "red")

Gives: