[R] Importing vector graphics into R

[(Ted Harding)]

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).

> 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!)]


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E-Mail: (Ted Harding) <Ted.Harding at nessie.mcc.ac.uk>
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Date: 08-Dec-04                                       Time: 13:47:12
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