On Tue, 1 May 2007, Jim Lemon wrote: > Paulo Barata wrote: >> 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? >> > Hi Paulo, > I may be misunderstanding you, but have you tried to increase the number > of segments in the arc using the "n" argument? > > draw.arc(1,1,1,n=100)
Put it another way, drawing arcs is not a primitive in the R graphics system but drawing circles is. So there is no low-level way to draw an arc of a circle except via line segments. (Quite a few graphics devices draw circles via line segments, but not all and vector-graphics systems like postscript can often do better.) -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.