[R] Importing vector graphics into R

[Roger Bivand]

On Wed, 8 Dec 2004 Ted.Harding at nessie.mcc.ac.uk wrote:

> On 08-Dec-04 Roger Bivand wrote:
> > On Tue, 7 Dec 2004, Hinrich Göhlmann wrote:
> > 
> >> Dear R users,
> >> 
> >> I know of the possibility to import bitmaps via the nice
> >> pixmap library. 
> >>     But if you later on create a PDF it is somewhat
> >> disappointing to have such graphics bitmapped. Is there
> >> a trick (via maps?) to import a vector graphic and have
> >> them plotted onto a graph? My searching attempts in the
> >> searchable r-help archive did not seem to result in anything 
> >> useful...
> > 
> > No, nothing obvious. If you have an Xfig file - or convert to
> > one from PS,
> 
> How does one do that? None of the tools I can find on my (Linux)
> system seem to include the possibility of PS->Xfig (or any other
> vector format either, except of course PDF).

http://www.pstoedit.net/pstoedit

currently maintained and fairly reliable.

> 
> > you may be able to extract the lines with their attributes by
> > hand (the file is just text, so you can "see" the vector
> > graphics), and write an R function to plot them (rescaled) onto
> > the device if you need a single graphical element many times.
> > Otherwise, perhaps edit the graphics file after R has completed
> > its work. None of the vector map formats is easy to use for
> > this kind of trick, especially because you probably need
> > attributes on the lines (thickness, colour).
> 
> When I first saw Hinrich's post, I thought it was a hopeless
> quest. Even if one had a PS file (rather than PDF), I think
> it would only be feasible to write such a conversion if it
> were guaranteed that the PS file used only "raw" PS language
> in its simplest usage (i.e. one would be able to look out for,
> and then interpret, the basic drawing commands like "moveto",
> "rmoveto", "lineto", "rlineto", etc. with explicit numerical
> coordinates). Unfortunately, many programs which output PS
> have extended preambles in which all sorts of abbreviations
> are defined to wrap up chunks of "raw" PS. So one would be
> looking at writing a fully featured PS interpreter!
> 
> When starting from a PDF file, however, even though this is
> in a sense "reminiscent" of PS (and may have been converted
> from a PS file), nevertheless PDF is a harder format to interpret
> because of its hierarchical "modular" construction (in effect
> a "tree of objects"). So I would be even less optimistic about
> coverting PDF to a non-PS vector format.
> 
> However, if I'm at all wrong about any of that I would be most
> interested to be informatively corrected!
> 
> On the other hand, there is the possibility to convert a bitmap
> to a PS file where lines and curves are drawn using vector
> graphics (giving the advantage that the result is as smooth as
> the resolution of the ultimate raster device allows, and also
> that the resulting file may be much smaller, since it only takes
> a few bytes to define a line or curve, while the corresponding
> bitmap may take many).
> 
> A very useful program for this purpose is 'autotrace': see
> 
>   http://autotrace.sourceforge.net/
> 
>   "Here is a short description of currently supported formats:
> 
>       * Inputformats BMP, TGA, PNM, PPM, PGM, PBM and those
>         supported by ImageMagick.
>       * Exportformat Postscript, svg, xfig, swf, pstoedit, emf,
>         dxf, cgm, mif, p2e and sk"
> 
> I also received the following just over a year ago on the
> 'autotrace' list, but the site does not respond now:
> 
> >  > What I really want, is a program like autotrace to output
> >  > a list of splines or some mathematical representation of
> >  > the image that I can  manipulate mathematically.
> >
> >  Maybe you'd like to have a look at this, to see what can be
> >  achieved with ~12 KB code (Don't laugh at me ;-) This program
> >  is actually used in production right now.)
> >
> >    http://www.mesw.de/stencil/
> 
> The "image that I can manipulate mathematically" sounds like 
> the sort of thing that Hinrich is looking for!
> 
> Best wishes to all,
> [autotraced signature attached (PDF -- note the size!)]
> 
> 
> --------------------------------------------------------------------
> E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
> Fax-to-email: +44 (0)870 094 0861  [NB: New number!]
> Date: 08-Dec-04                                       Time: 13:47:12
> ------------------------------ XFMail ------------------------------
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Breiviksveien 40, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 93 93
e-mail: Roger.Bivand at nhh.no