I should have been much more specific with my question and supplied an
example.
In the meantime I believe I found the solution in the PBSmapping package,
this time I will provide an example that illustrates what I am trying to
achieve:

#Get the boundaries for Manhattan:
library(maps);
library(PBSmapping);
Manhattan <- map('county', 'new york,new york', plot=F);
#define a few points in Manhattan and compute the corresponding Voronoi
regions:
XY <- cbind.data.frame( PID = 1, POS = 1:10,
         X =
c(-73.97220,-73.95456,-73.97906,-73.98685,-73.99968,-73.96716,-73.97127,-73.96524,-73.98322,-74.00587),
 Y =
c(40.74983,40.77402,40.75022,40.73952,40.72842,40.75677,40.75112,40.75513,40.76271,40.74026)
);
polys <- calcVoronoi(as.PolySet(XY, projection="LL") );
#plot the Voronoi regions:
plotMap(polys)
#It would be a much more meaningful plot to clip these Voronoi regions to
the Manhattan boundaries:
m <- as.PolySet (cbind.data.frame(PID = 1, POS = 1:length(Manhattan$x),  X =
Manhattan$x, Y = Manhattan$y))
plotMap(joinPolys(m, polys, "INT" ), xlim = Manhattan$range[1:2], ylim =
Manhattan$range[3:4]);

So the key operation I was looking for was simply the intersection provided
by the function (joinPolys(..., "INT" ) from PBSmapping.

Thanks again,
Markus


On Sun, Feb 21, 2010 at 8:26 AM, Roger Bivand <Roger.Bivand@nhh.no> wrote:

> On Sun, 21 Feb 2010, Markus Loecher wrote:
>
>  Dear all,
>> I apologize if this is too simple a question as it does appear to be a
>> basic
>> GIS operation but I have not found the appropriate function that performs
>> a
>> clipping of polygons into boundaries given by a (larger "outer") polygon.
>> I
>> tried overlay() from package sp and clipPolys from package PBSmapping but
>> none converted the "inner" polygons into new ones laying inside the
>> boundaries given by the outer polygon.
>>
>
> Maybe a basic GIS operation should be done in a GIS? Otherwise, please feel
> free to consult threads on the license problems of gpclib, and about the
> R-forge rgeos package. If you'd like to contribute such an intersection (I
> think you want the intersection between an arbitrary SpatialPolygons object
> and a simple SpatialPolygons object for the outer polygon) function tool to
> rgeos, or at least a sketch of how it might work, that would be helpful.
>
> Roger
>
>
>> Any help would be greatly appreciated,
>> Thanks,
>>
>> Markus
>>
>>        [[alternative HTML version deleted]]
>>
>> _______________________________________________
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>> R-sig-Geo@stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
>>
>>
> --
> 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@nhh.no
>
>

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