On 8/09/2009, at 11:58 AM, Juan Alonso wrote:
Hello,
Please take a look at the attached plot and let me know if this is
normal. The circle has radio I am using R 2.9.2 inside OS X Leopard.
The plot was generated with:
png('bizarre_circle.png')
plot(c(-5,0,0,5), c(0,5,-5,0))
symbols(0,0, circles=c(sqrt(25)), inches=FALSE, add=TRUE)
dev.off()
<snip>
Please don't post implied criticism of software (``very inaccurate'')
when the fault lies not in the software but in your understanding.
There is *nothing* inaccurate about the circles. The symbols() function
is cleverly designed to produce ``circles'' that ***look*** like circles
when plotted. In most cases they ***aren't*** circles, but rather
ellipses,
with eccentricity adjusted to compensate for the aspect ratio of the
plot
on which they are being superimposed.
If you want the symbols()-created circle to pass through points which
really
do lie on a circle you need to make the aspect ratio of the plot
equal to 1:
plot(c(-5,0,0,5), c(0,5,-5,0),asp=1)
symbols(0,0, circles=c(sqrt(25)), inches=FALSE, add=TRUE)
OMMMMMMMMM!
cheers,
Rolf Turner
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