[R-sig-Geo] conversion to polygons

[Roger Bivand]

On Fri, 16 Jun 2006 pedro at dpi.inpe.br wrote:

> Hi,
> 
> I also have same "problem". Sometimes I want to build a SpatialPolygons 
> from a set of points (a matrix) representing the border of a region, 
> and it has only one polygon.
> 
> SP <- SpatialPolygons(list(Polygons(list(Polygon(matrixdata))),ID=1)))
> 
> But ID in this case is not "necessary", and also the two levels of 
> list. At least for me, it is very common, and I can cite geoR and 
> splancs packages, where we have this kind of data. I think in this case 
> we could have a simpler code, and we could create it directly from the 
> matrix:
> 
> SP = SpatialPolygons(matrixdata)
> 
> or from the Polygon:
> 
> SP = SpatialPolygons(polygon)
> 
> The creation of the lists and ID could be hidden in SpatialPolygons-methods.R:
> 
> SpatialPolygons <- function(Srl, pO, proj4string=CRS(as.character(NA))) {
>      if( is.matrix(Srl) ) Srl <- list(Polygons(list(Polygon(Srl))),ID=1))
>      ...
> }
> 
> What do you think of it?

Yes, good idea, I'll implement it once useR 2006 is over for 
SpatialPolygons and Spatial Lines.

Thanks, Roger

> 
> Pedro
> 
> Quoting Roger Bivand <Roger.Bivand at nhh.no>:
> 
> > On Wed, 14 Jun 2006, Luis Ridao Cruz wrote:
> >
> >> R-Sig-Geo help,
> >>
> >> I have an objct of class "SpatialPointsDataFrame"
> >> which I woul like to convert to polygon.
> >>
> >> I have used the following:
> >>
> >> test1<-Polygon(test)
> >> test2<-SpatialPolygons(list(test),1)
> >
> > test2<-SpatialPolygons(list(Polygons(list(test)),ID=1)))
> >
> > should do it - there are two layers, because some "Polygons" objects with
> > a single ID can have multiple "Polygon" object members.
> >
> > Roger
> >
> >> plot(test2,col=2,pbg="white")
> >>
> >> but I get en error message like this:
> >>
> >> Error in as.list(X) : cannot get a slot ("Polygons") from an object of
> >> type "double"
> >>
> >> I also try ploting:
> >>
> >> plot(test1)
> >>
> >> which gives :
> >>
> >> Error in plot.window(xlim, ylim, log, asp, ...) :
> >>         need finite 'xlim' values
> >> In addition: Warning messages:
> >> 1: no non-missing arguments to min; returning Inf
> >> 2: no non-missing arguments to max; returning -Inf
> >> 3: no non-missing arguments to min; returning Inf
> >> 4: no non-missing arguments to max; returning -Inf
> >>
> >>
> >>
> >>
> >> Thank you in advance
> >>
> >> _______________________________________________
> >> R-sig-Geo mailing list
> >> R-sig-Geo at 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 at nhh.no
> >
> > _______________________________________________
> > R-sig-Geo mailing list
> > R-sig-Geo at stat.math.ethz.ch
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
> 
> 
> 
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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