[gdal-dev] problem with CloseRings

Wed Aug 22 10:27:46 PDT 2012

Doug,

You could rebuild individual polygons by attempting to close the
constituent rings one-by-one while discarding those that give an error with
the CloseRings() method.

On Wed, Aug 22, 2012 at 10:41 PM, <Doug_Newcomb at fws.gov> wrote:

>
> Oliver,
>
> Would it just be a matter of counting the vertices of each polygon,
> selecting the polygons with 3 vertices, and comparing the value of the
> first and last vertex  as you are building wkt value string below?
>
>
> Doug
>
>
>
> >The problem with your rings isn't that they are not closed, it is that
> >they are degenerate.
>
> >For instance:
> >(559560.19 142169.94,559550.64 142173.43,559560.19 142169.94)
>
> >This goes from PointA to PointB back to PointA.  It is closed, it just
> >is degenerate.  It has no area.  I'm not aware of a super easy way of
> >cleaning out such junk rings - you might need to explicitly test them
> >and remove them if they are degenerate.
>
> >Best regards,
>
>
>
>
> Doug Newcomb
> USFWS
> Raleigh, NC
> 919-856-4520 ext. 14 doug_newcomb at fws.gov
>
> ---------------------------------------------------------------------------------------------------------
> The opinions I express are my own and are not representative of the
> official policy of the U.S.Fish and Wildlife Service or Dept. of the
> Interior.   Life is too short for undocumented, proprietary data formats.
>
>
>  *Frank Warmerdam <warmerdam at pobox.com>*
> Sent by: gdal-dev-bounces at lists.osgeo.org
>
> 08/22/2012 12:49 PM
>   To
> Oliver Christen <oliver.christen at camptocamp.com>
> cc
> gdal-dev at lists.osgeo.org
> Subject
> Re: [gdal-dev] problem with CloseRings
>
>
>
>
> Oliver,
>
> The problem with your rings isn't that they are not closed, it is that
> they are degenerate.
>
> For instance:
> (559560.19 142169.94,559550.64 142173.43,559560.19 142169.94)
>
> This goes from PointA to PointB back to PointA.  It is closed, it just
> is degenerate.  It has no area.  I'm not aware of a super easy way of
> cleaning out such junk rings - you might need to explicitly test them
> and remove them if they are degenerate.
>
> Best regards,
>
> On Wed, Aug 22, 2012 at 9:13 AM, Oliver Christen
> <oliver.christen at camptocamp.com> wrote:
> > dear community
> >
> > first of all please accept my apologies if this is not the correct
> > place to ask about such question.
> >
> > I am trying to manipulate some geometric data using the gdal/ogr
> > python lib and Im facing a problem when trying to transform invalid
> > ring into valid ring.
> >
> > I have polygons with unclosed holes and I expected the CloseRings
> > function to solve this for me, but unfortunately, that functions
> > doesnt seem to do anything (in my case).
> >
> > see below for a simply python testcase,
> >
> > if you could tell me if I am possibly not using that function
> > correctly or if there is a more correct way to do that, you would be
> > very welcome
> >
> > using python version 2.6.6
> > osgeo ogr lib version 1.3.40
> >
> > thank you very much for your attention
> > best regards
> > Oliver
> >
> > from osgeo import ogr
> >
> > wkt = "POLYGON ((559577.81 142165.04,559577.67 142161.79,559577.66
> > 142161.16,559577.18 142139.0,559564.07 142140.84,559562.99
> > 142132.4,559556.42 142134.85,559556.47 142134.96,559541.39
> > 142140.58,559549.54 142162.4,559547.0200406529475
> > 142163.310114102292573,559550.570425555342808
> > 142173.455536680703517,559577.81 142165.04),(559559.95600777247455
> > 142169.280249390256358,559550.996165407239459
> > 142172.552877245907439,559550.996165407355875
> > 142172.552877245907439,559547.909677243907936
> > 142163.733065433305455,559550.443360350676812
> > 142162.817994827404618,559542.290859716595151
> > 142140.991299878398422,559557.417905980604701
> > 142135.353766721702414,559557.367843619547784
> > 142135.243629527511075,559562.407678314950317
> > 142133.364239115995588,559563.465598454349674
> > 142141.631689094298054,559576.497222575126216
> > 142139.80268921770039,559576.960120304953307
> > 142161.173134415294044,559576.970239149406552
> > 142161.810621617711149,559577.084823867655359
> > 142164.470624003995908,559577.084823867655359
> > 142164.470624004025012,559570.876975534367375
> > 142165.896950183814624,559564.754505693446845
> > 142167.653979024267755,559564.75450569356326
> > 142167.653979024296859,559559.956007772590965
> > 142169.280249390256358,559559.95600777247455
> > 142169.280249390256358),(559560.19 142169.94,559550.64
> > 142173.43,559560.19 142169.94),(559564.97 142168.32,559560.19
> > 142169.94,559564.97 142168.32),(559577.810000000172295
> > 142165.04,559571.34395208011847 142166.499739240010967,559564.97
> > 142168.32,559577.810000000172295 142165.04))"
> >
> > poly = ogr.CreateGeometryFromWkt(wkt)
> >
> > poly.IsValid()
> > ERROR 1: IllegalArgumentException: Invalid number of points in
> > LinearRing found 3 - must be 0 or >= 4
> > False
> >
> > poly.CloseRings()
> >
> > poly.IsValid()
> > ERROR 1: IllegalArgumentException: Invalid number of points in
> > LinearRing found 3 - must be 0 or >= 4
> > False
> > _______________________________________________
> > gdal-dev mailing list
> > gdal-dev at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/gdal-dev
>
>
>
> --
>
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam,
> warmerdam at pobox.com
> light and sound - activate the windows |
> <http://lists.osgeo.org/mailman/listinfo/gdal-dev>
> http://pobox.com/~warmerdam
> and watch the world go round - Rush    | Geospatial Software Developer
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-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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