[R] to draw a smooth arc

[Paulo Barata]

Dear R-list members,

I would like to draw a smooth arc. I can draw an arc
parametrically, but this produces an arc too coarse,
even allowing for different increments in sequence t
in the example below. Function "symbols" (graphics) does
produce a smooth circle, but it cannot produce an arc.

Please see the following example, drawing complete circles:

plot(-5:5,-5:5,type='n')
## draws circle with function symbols (package graphics)
## - inner circle is very smooth:
symbols(0,0,circles=2,add=TRUE)
## draws circle parametrically - outer circle is too coarse:
pi <- 4*atan(1)
t <- seq(0,2*pi,0.02)
lines(4*cos(t),4*sin(t))

Package "plotrix" has a function "draw.arc", but arcs produced
with this function are also either too coarse or too polygonal,
depending on the number of polygons used to approximate the arc.

Is there a way to harness the characteristics of function
"symbols" (graphics) to draw a smooth arc, not just a complete
circle?

I am using R 2.5.0, running under Windows XP.

Thank you very much.

Paulo Barata

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Paulo Barata
Fundacao Oswaldo Cruz (Oswaldo Cruz Foundation)
Rua Leopoldo Bulhoes 1480 - 8A
21041-210  Rio de Janeiro - RJ
Brazil
E-mail: pbarata at infolink.com.br