From: Paulo Barata <pbarata_at_infolink.com.br>

Date: Tue, 01 May 2007 18:57:10 -0300

Paul Murrell wrote:

*> Hi
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*>
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*>
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> Paulo Barata wrote:

*>
*

*>
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> Just to back up a few previous posts ...

*>
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*> There is something like this facility already available via the
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*> grid.xspline() function in the grid package. This provides very
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*> flexible curve drawing (including curves very close to Bezier curves)
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*> based on the X-Splines implemented in xfig. The grid.curve() function
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*> provides a convenience layer that allows for at least certain
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*> parameterisations of arcs (you specify the arc end points and the angle).
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*>
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*> These functions are built on functionality within the core graphics
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*> engine, so exposing a similar interface (e.g., an xspline() function)
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*> within "traditional" graphics would be relatively straightforward.
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*>
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*> The core functionality draws the curves as line segments (but
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*> automatically figures out how many segments to use so that the curve
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*> looks smooth); it does NOT call curve-drawing primitives in the
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*> graphics device (like PostScript's curveto).
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*>
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*> In summary: there is some support for smooth curves, but we could still
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*> benefit from a specific arc() function with the standard
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*> centre-radius-angle parameterisation and we could also benefit from
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*> exposing the native strengths of different graphics devices (rather than
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*> the current lowest-common-denominator approach).
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*>
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*> Paul
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*>
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*>
*

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. Received on Tue 01 May 2007 - 22:02:54 GMT

Date: Tue, 01 May 2007 18:57:10 -0300

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().

Thank you.

Paulo Barata

Paul Murrell wrote:

> 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 ...

>> 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_at_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. > ______________________________________________R-help_at_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. Received on Tue 01 May 2007 - 22:02:54 GMT

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