[R-sig-Geo] Help with gpclib

[Roger Bivand]

On Thu, 19 Jul 2012, hadley wickham wrote:

>> The chief problem is the totally unnecessary use of gpclib in fortify() in
>> ggplot2. gpclib should never, ever be used, as its licence only permits
>> hobby use to learn about polygon clipping - imposed against the author's
>> will by his former university. The rgeos package provides all functionality
>> provided by gpclib except breaking polygons into component triangles, which
>> is not relevant here. Specifically, ggplot2/R/fortify-spatial.R says (l.
>> 33-5):
>>
>>   # Union together all polygons that make up a region
>>   try_require(c("gpclib", "maptools"))
>>   unioned <- unionSpatialPolygons(cp, invert(polys))
>
> That code is out of date. The current code is
> https://github.com/hadley/ggplot2/blob/master/R/fortify-spatial.r

The released code is as quoted, which is what users see. I think github 
does not provide automatic check, build, and binary build of development 
versions of packages (like R-forge). So users cannot install from github 
without checking out the source code?

>
> That only uses try_require("maptools") (and only if you use a
> non-default grouping). As far as I know, that should automatically
> pick between gpclib and rgeos depending on which is installed.
>

Exactly. This will only fail if non-default grouping is requested and 
neither gpclib nor rgeos are available.

> Despite the license for gpclib making it only suitable for
> "hobbyists", it is much easier to install than rgeos, which requires
> an external install.

Not "much easier", for all Windows and OSX users installing CRAN binary 
packages, there is now, thanks to Brian Ripley, Uwe Ligges, and Simon 
Urbanek, no difference at all. GEOS is available as a binary install for 
most popular Linux versions, from there a source install of rgeos is no 
harder than other source packages with external dependencies (like XML).

The gpclib licence is rather perverse (and the link on the CRAN package 
page dead, the href includes a semicolon):

http://www.cs.man.ac.uk/~toby/gpc/

"GPC Licensing

GPC is free for downloading and time-unlimited evaluation by anyone.

Non-commercial use of GPC (for example: private / hobbyist / education)

GPC is free for non-commercial use only.
We invite non-commercial users to make a voluntary donation towards the 
upkeep of GPC.

Commercial use of GPC (for example: product development / commercial 
research)

If you wish to use GPC in support of a commercial product,
you must obtain an official GPC Commercial Use Licence from The University 
of Manchester. Please email for details."

I have seen a definition of "education" as self-learning only, but cannot 
trace it; it is not "free software" for non-commercial use in the "normal" 
(ACM?) sense. I consider that using it in taught courses for which payment 
is received to be borderline (for example useR! tutorials), possibly on 
the wrong side of the border. Simply avoid gpclib!

Roger

>
> Hadley
>
>

-- 
Roger Bivand
Department of Economics, NHH Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no