Hi
Paulo Barata wrote: > Dr. Murrell and all, > > One final suggestion: a future function arc() in package graphics, > with centre-radius-angle parameterisation, could also include an > option to draw arrows at either end of the arc, as one can find > in function arrows(). ... and in grid.xspline() and grid.curve(). Paul > Thank you. > > Paulo Barata > > ----------------------------------------------------------------------- > Paul Murrell wrote: >> Hi >> >> >> Paulo Barata wrote: >>> Dr. Snow and Prof. Ripley, >>> >>> Dr. Snow's suggestion, using clipplot (package TeachingDemos), >>> is maybe a partial solution to the problem of drawing an arc of >>> a circle (as long as the line width of the arc is not that large, >>> as pointed out by Prof. Ripley). If the arc is symmetrical around >>> a vertical line, then it is not so difficult to draw it that way. >>> But an arc that does not have this kind of symmetry would possibly >>> require some geometrical computations to find the proper rectangle >>> to be used for clipping. >>> >>> I would like to suggest that in a future version of R some function >>> be included in the graphics package to draw smooth arcs with >>> given center, radius, initial and final angles. I suppose >>> that the basic ingredients are available in function "symbols" >>> (graphics). >> >> Just to back up a few previous posts ... >> >> There is something like this facility already available via the >> grid.xspline() function in the grid package. This provides very >> flexible curve drawing (including curves very close to Bezier curves) >> based on the X-Splines implemented in xfig. The grid.curve() function >> provides a convenience layer that allows for at least certain >> parameterisations of arcs (you specify the arc end points and the angle). >> >> These functions are built on functionality within the core graphics >> engine, so exposing a similar interface (e.g., an xspline() function) >> within "traditional" graphics would be relatively straightforward. >> >> The core functionality draws the curves as line segments (but >> automatically figures out how many segments to use so that the curve >> looks smooth); it does NOT call curve-drawing primitives in the >> graphics device (like PostScript's curveto). >> >> In summary: there is some support for smooth curves, but we could still >> benefit from a specific arc() function with the standard >> centre-radius-angle parameterisation and we could also benefit from >> exposing the native strengths of different graphics devices (rather than >> the current lowest-common-denominator approach). >> >> Paul >> >> >>> Thank you very much. >>> >>> Paulo Barata >>> (Rio de Janeiro - Brazil) >>> >>> ----------------------------------------------------------------------- >>> Prof Brian Ripley wrote: >>>> On Tue, 1 May 2007, Greg Snow wrote: >>>> >>>>> Here is an approach that clips the circle you like from symbols down to >>>>> an arc (this will work as long as the arc is less than half a circle, >>>>> for arcs greater than half a circle, you could draw the whole circle >>>>> then use this to draw an arc of the bacground color over the section you >>>>> don't want): >>>>> >>>>> library(TeachingDemos) >>>>> plot(-5:5, -5:5, type='n') >>>>> clipplot( symbols(0,0,circles=2, add=TRUE), c(0,5), c(0,5) ) >>>> I had considered this approach: clipping a circle to a rectangle isn't >>>> strictly an arc, as will be clear if the line width is large. >>>> Consider >>>> >>>> clipplot(symbols(0, 0 ,circles=2, add=TRUE, lwd=5), c(-1,5), c(-1,5)) >>>> >>>> Note too that what happens with clipping is device-dependent. If R's >>>> internal clipping is used, the part-circle is converted to a polygon. >>>> >>>> >>> ______________________________________________ >>> 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. -- Dr Paul Murrell Department of Statistics The University of Auckland Private Bag 92019 Auckland New Zealand 64 9 3737599 x85392 [EMAIL PROTECTED] http://www.stat.auckland.ac.nz/~paul/ ______________________________________________ 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.