[R-sig-Geo] ring not closed - readShapePoly - read.shape - maptools

[Roger Bivand]

On Sat, 10 Feb 2007, Susumu Tanimura wrote:

> Hi there,

> The same problem happened to me when I used the shape file that is
> sold as commercial products.

> > getinfo.shape("Phu_Yen_Commune_ll_region.shp")
> Shapefile type: Polygon, (5), # of Shapes: 104
> a <- read.shape("Phu_Yen_Commune_ll_region.shp")
> Field name:  1__PERS  changed to:  X1__PERS 
> Field name:  2_PERS  changed to:  X2_PERS 
> Field name:  3_PERS  changed to:  X3_PERS 
>        [snip]
> Shapefile type: Polygon, (5), # of Shapes: 104
> > b <- readShapePoly("Phu_Yen_Commune_ll_region.shp",verbose=TRUE)
> Field name:  1__PERS  changed to:  X1__PERS 
> Field name:  2_PERS  changed to:  X2_PERS 
> Field name:  3_PERS  changed to:  X3_PERS 
>        [snip]
> Shapefile type: Polygon, (5), # of Shapes: 104
> Error in validityMethod(object) : ring not closed

> So, read.shape seems to be OK, but readShapePoly does not.  Since
> readShapePoly uses internally read.shape and then Map object is passed
> to .Map2PolyDF(), I tried to find Map2PolyDF or validityMethod in
> source of maptools and sp package.  However, I could not find them.

> Dose anybody have better solution?

Patrick, Susumu,

Could (either or both) you please make sample files available? I think 
that readOGR() will do the same as readShapePoly(), even though it does 
not use the same intermediate R code (same shapelib code in OGR). The 
internal function .Map2PolyDF can be accessed inside the maptools 
namespace as maptools:::.Map2PolyDF; it calls 
maptools:::.asSpatialPolygonsShapes, calling maptools:::.shp2srsI. This 
calls Polygon() with coords set to the current ring, so if it isn't 
closed, no check is made. It would be possible to pass an argument through 
closing unclosed rings if TRUE, default FALSE.

Best wishes,

Roger


> OK... after a check, none of the rings are closed... suppose closing was 
> managed automatically by ArcGIS and read.Shape...
> 
> 
> Patrick Giraudoux a écrit :
> > Hi,
> >
> > I have slept on some data of a project which started in 2003 and  just 
> > coming back on them today gives the opportunity to compare read.shape 
> > (shapefiles were initially imported with this function) and 
> > readShapePoly (the new one sp style). The latter will be much more 
> > interesting for the next step, giving directed handling to overlay 
> > methods.
> >
> > Importing one of my shapefile with read.shape ( read as polyshape in 
> > ArcGIS) made (and still makes) no problem. However, when I try to 
> > import it again via readShapePoly, I get this message:
> >
> > > UG<-readShapePoly("U:/Documents and Settings/giraudoux/Mes 
> > documents/FC25/NewSIG050317/UG.shp")
> > Error in validityMethod(object) : ring not closed
> >
> > Clear enough: at least one of the polygons is not closed... which is 
> > confirmed by the fact that I can import the shapefile easy with 
> > readShapeLines. I suppose the readShapePoly is more demanding in 
> > validity control than the older read.Shape and ArcGIS: one cannot 
> > complain for that.
> >
> > I am not afraid of sorting this out with some lines of programme. I 
> > have however a question before writing it: is there already a function 
> > making a check somewhere which could be used to know which one(s) of 
> > the polygons are not closed?
> >
> > Patrick

--
Susumu Tanimura MSc PhD
Dept. of Socio-environmental Medicine
Inst. of Tropical Medicine, Nagasaki University
TEL +81-95-849-7865 FAX +81-95-849-7867
e-mail stanimura-ngs at umin.ac.jp

_______________________________________________
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