[R] Shapefiles

[Roger Bivand]

On Thu, 9 Feb 2006, Tarmo Remmel wrote:

> Dear List,
> 
> I have examined the sp, maptools, and shapefiles packages (Windows) but
> cannot seem to figure out a solution for writing shapefiles for 'curvy
> shapes'.  The scenario is that I generate a series of polygons, circles, and
> ellipses on a plot and would like to convert them to shapefiles.  Since the
> circles and ellipses are do not return a coordinate list during the plotting
> sequence (e.g., all I need supply are the lengths of axes and rotation
> angle), is there an easy way by which the plot window can be converted to a
> shapefile?

No, the plot window is committed to the device, and (re)-capturing the 
objects there as polygon objects will be messy. You'll need to generate an 
object that can be drawn as a sequence of straight line segments, and 
create a polygon object from that, from the x,y coordinates of the centre 
and the radius, or major/minor axes lengths and orientations. There is 
some code on:

http://finzi.psych.upenn.edu/R/Rhelp02a/archive/56190.html

(see RSiteSearch("circle"))

but I don't know if it will suit your purposes. Once constructed, the 
polygons can be built into an object for exporting.

> 
> Thank you,
> 
> Tarmo
> 
> __________________________________________
> Tarmo Remmel  Ph.D.
> GUESS Lab, Department of Geography
> University of Toronto at Mississauga
> Mississauga, Ontario, L5L 1C6
> Tel: 905-569-4382
> Lab: 905-828-3868
> Fax: 905-828-5273
> Skype: tarmoremmel
> http://eratos.erin.utoronto.ca/remmelt
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, 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