ring not closed - readShapePoly - read.shape - maptools

A new package, spsurvey, has function to read ESRI shapefiles -
read.shape and read.dbf.  The result is an sp spatial object.  The
functions read point, line, and polygon shapefiles.  package is on CRAN.
We have encountered all types of issues with shapefiles so may handle
your problem.

Tony



                                                                        
             Roger Bivand                                               
             <Roger.Bivand at nh                                           
             h.no>                                                   To 
             Sent by:                 Susumu Tanimura                   
             r-sig-geo-bounce         <stanimura-ngs at umin.ac.jp>        
             s at stat.math.ethz                                        cc 
             .ch                      r-sig-geo at stat.math.ethz.ch,      
                                      patrick.giraudoux at univ-fcomte.fr  
                                                                Subject 
             02/09/2007 10:35         Re: [R-sig-Geo] ring not closed - 
             AM                       readShapePoly - read.shape -      
                                      maptools                          
                                                                        
              Please respond                                            
                    to                                                  
             Roger.Bivand at nhh                                           
                   .no

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 ??crit :

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

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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

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