Thanks!
Including the fill = True line in map made things work.  (I needed the
PolySet to run a Dirichlet tesselation).



On Thu, Nov 25, 2010 at 10:10 AM, Roger Bivand <Roger.Bivand@nhh.no> wrote:

> On Thu, 25 Nov 2010, Ted Rosenbaum wrote:
>
>  Hi:
>> When I run the following command to convert a US state polygon from the
>> maps
>> package to a polyset in PBSmapping, I obtain extra lines that should not
>> be
>> in there.
>>
>> plotMap(SpatialLines2PolySet(map2SpatialLines(map('state','maryland',interior=FALSE),proj4string=CRS("+proj=longlat
>> +datum=wgs84"))))
>> Compare to :
>> map('state','maryland').
>> I appreciate anyone's insight as to why this conversion is not working.
>>
>
> map() and plootMap() have different pen-up and pen-down conventions. The
> easiest correction is:
>
> md <- map('state','maryland',interior=FALSE, plot=FALSE, fill=TRUE)
> spmd <- map2SpatialLines(md)
> xx <- SpatialLines2PolySet(spmd)
> plotMap(xx)
>
> where fill=TRUE reverses those lines that do not connect. I think that a
> PolySet thinks that it is a polygon, with fill=FALSE you get 11 lines, which
> although they are converted correctly with correct PID, seem to be closed by
> plotMap(). Indeed, using plotLines() instead of plotMap() achieves the
> effect you want (but with an odd axis artefact - plotLines() probably
> assumes that it is being added to an existing plot, and doesn't seem to set
> aspect correctly), plotMap() imposes the assumption that you have polygons.
>
> Why not just plot(spmd)? Are you sure about the datum in your spatial
> reference (if it matters for you)?
>
> Roger
>
>
>  Thanks very much!
>>
>> ---------------------------------------------
>> Ted Rosenbaum
>> Graduate Student
>> Department of Economics
>> Yale University
>>
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>>
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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@nhh.no
>
>

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